I had to do a Percy Jackson fic, about this. Our Pastry Bomber is rather unique. The Mysteriously Appearing Baked Goods character was inspired by a story by writer HecateA. Go read their writing. They're Amazing!
Percy Jackson and the Olympians belongs to Rick Riordan, and last time I checked,my first name wasn't Rick, my last name wasn't Riordan, and I wasn't a guy.

Chiron and Dionyses where staring at the objects on the table like they had just fallen from the sky.
For all intents and purposes, the massive tray of cupcakes had fallen from the sky – although that had been ruled out due to all the cupcakes being in perfect condition.
"Whoever made these knows a lot about the camp and campers." Chiron sighted "Look there are enough cupcakes for each camper to have one, they're specilized for each cabin, each cupcake even has a camper's name on it, and if last weeks where any indicator, the flavors are also personalized." Chiron turned to Dionyses "Do you know who is leaving these?"
"Maybe it was Aunt Deter?"
"Lady Demeter would have included bran or cereal of some kind. There isn't any. What about Lady Hestia?
"The cupcakes are too intercate for Aunty and besides those two I don't think anyone in my family can cook."

The two return to staring at the pastries like they had fallen from the sky. Indeed they were very intricate cupcakes, and styled after the demigod's parent. The Apollo cabin's featured eddible instrument, the Hephestus cabin's had moving parts, Nico's was decorated with what was probebly a mexican dancing skeleton, and Percy's was blue, and covered with swedish fish.
Finally after at least ten more minutes Dionyses streched saying " Well, I'm going to bed. Make Perry and Annibell sit up and watch for our cupckae maker."
One Week Later…

"So we have to stay up all night watching for someone to leave a try of cupcakes. Why?" Percy turned his head to look at Annabeth, who was absorbed in Dadules's laptop.
"As Chiron said, whoever is leaving behind these cupcakes is doing so without effecting the camp's borders Percy. Chiron needs to know who they are and how they are doing it."
"Ok, so why do WE have to stay up?"
"I have no idea Percy. Let me work."

Hours ticked by or maybe it was minutes. It was hard to tell when time moved at a rate comparable to the last day of school or a long car ride. However after an uncertin amount of time, a slight cloaked figure slipped into the dinning pavillion. Annabeth elbowed Percy, to wake him up, as in the uncertin period of time he had fallen asleep.
The cloaked figure glided to the center of the room, carrying a large plate of cupcakes in her – the figure was definatly female- arms. As she place the tray on one of the tables, Percy and Annabeth emerged from the shadows weapons drawn.
"Excuse me." Annabeth said "Who are you?" The figure whirled around, and as she did her hood fell back revealing long curly black hair. As she came around to face them, the golden circlet that was in her hair caught the light, and glittered.
Annabeth and Percy jumped back as they met the woman's eyes. Her eyes were molten gold, much like Kronos's and the other Titan's eyes had been.
"Oh! I'm so sorry for frightening you." The woman smoothed back her hair, and smoothed down her cloak. "I didn't expect any of my great grandchildren to be here." she looked back up at them correcting herself. "great grand children, and grand children. I just felt that I had to do something for you kids, after all you've been through."
Annabeth's eyes where racing at a thousand miles a minute. "Are you Lady Rhea? The Queen of the Titans." the woman laughted,
"Just Rhea sweety, or Grandma if you want. But yes, that's me."
"You're a lot nicer than your husband." Percy blurted out. Annabeth sighed, while Rhea made a face.
"Ex-husband Percy, ex-husband. I tracked him down and made him sign divorce papers, and since he has always been so bad at keeping track of his stuff – which is how Hades Posidon, and Zeus go their hands on his scythe in the first place – so I may have diluted the spells on his scythe. He never noticed, and unfortunatly Zeus seems to have inherited that trait, and Hera is too much like Mother for my liking, but I shouldn't be nitpicking them."
"Um Lady Rhea er I mean Rhea, why are you leaving us these cupcakes?" Annabeth asked as Rhea drifted off, her eyes far away.
"Oh, sweety, that's because I had to do something for you kids. You're all doing so much good, and your parents are not doing their jobs! I mean, you Percy shouldn't have had to ask them to claim their children, and they should be spending time with you, there is a difference between interfearing and spending time with someone! Also Kronos isn't in any position to apologise and even if he was, he simply is too proud to do so. I feel its my job as Queen of the Titans to fix the damage my husband won't." Suddenly Rhea clapped her hands "Oh! I almost forgot. I promised to give Hestia this, but I've been so busy. I know she loves to hang out around camp, so can you please give it to her for me." From under her cloak Rhea produced a small leather bound album. "This is all the childhood pictures of the second generation Olympians, you know Artemis, Pheobus, Hermes, ectra. Oh, and you should take a look at them. They all were just precious! Also, please remind Chiron to watch his sodium intake, he forgets sometimes."
With that Rhea pulled both Percy and Annabeth into a hug saying, "Bye kiddos! I hope to see you soon." she then handed Annabeth the album, and vanished. After she was gone it took Percy and Annabeth a moment to recover.
"That was Rhea?" Percy asked nobody in particular. Annabeth looked a little daised
"I'd heard she was a lot like Hera, but Hestia seems to be a closer match personality wise."
"Hey, let me see that." Percy took the album from Annabeth. The page he opened up to showed two toddlers – Artemis and Apollo. Apollo was crying because she was shooting a toy bow at him. A frazled looking woman was trying to consul the sobbing child.
"The woman must be Leto, Artemis and Apollo's mom." Annabeth muttered, as they flipped through the album. The next page had a young child who could only Hermes being chased around by an upset Apollo, while Athena and Artemis were making a pillow fort in the background too keep out Ares, and Posidon could be seen in the background snoring; obviously he had given up trying to babysit the child gods.
"Wow, Rhea was right. They really were cute."

…
The Next Morning
"Thank you so much!" Hestia laughed smiling as Percy gave her the album. "Mom really has been busy, and I've wanted to get my hands on a copy, but Hermes hid all the ones on Olympus. I've also been trying to put together a teenage album of me and my siblings just after we beat dad, but Hera and Hades conspired to feed Cerberus all the photos."
"I hope you manage to find some. I'm sure Rhea might have them somewhere."
"Ya, Mom really is the personification of the phrase 'Mother Hen'. I'll be sure to call her." Hestia uncharactistically skipped off, waving goodbye.
"Well, I'm glad she's in a good mood." Percy said to Annabeth, "Now lets go tell Chiron who the Cupcake maker was."
Chiron had just taken the last culer out of his tail when Percy and Annabeth knocked on the door.
"Come in."
"Morning Chiron, we caught the person responsible for the cupcakes." Annabeth said "It was Lad- er Rhea."
"Oh, I really should have though of her. Rhea is generally behind mysteriously appearing baked goods, and this morning she arrived on Olympus in full Smoother mode, and she grounded all of her children, as an excuse to spend time with them. I suppose she asked you to remind me to watch my sodium intake."
"Maybe?"

And so the unoffical sequal of The Last Olympian (Percy Jackson and the Mysteriouslly Appearing Baked Goods) comes to the close. Rhea a much ignored character in the Classical Mythos was the culprit. No I'm serious, as far as I can tell her only traits are "Kronos's Wife/Sister" (which combind with the fact that Zeus and Hera are full siblings might explain the sanity levels of Olympus) and "Zeus's Mom". She barely gets mentioned in the Percy Jackson Series, and there are litterally like three stories on that have her as a character. If anyone is looking for another story with her HecateA's On a Scale of One to Ten has her appear. See you later.