FYI: Twilight's more like she was in 'Bird in the Hand' and "Lesson Zero" than in 'Luna Eclipsed'. I think she was far more entertaining and in character.
For Luna's Sake
Twilight Sparkle was quite happy to see that Princess Luna looked like the normal pony she was at the end of that fateful day Equestria was threatened with an eternity of night.
She looked like she could have been their age if not younger, though they all knew she was thousands of years old. Her face and posture spoke of her royal ranking and the immense power she possessed. But a close look into her ethereal eyes revealed a surprising resemblance to Fluttershy's, in both honesty and insecurity.
"Hi Princess Luna!" A gratingly high voice suddenly shouted very much too close to to Twilight's ear.
Pinkie Pie dashed over to the princess and had already accosted her by the time Twilight recovered from the echoing shout.
"Yeep-ee" Pinkie Pie shouted as she danced around Princess Luna. The forced polite smile Luna had when they first arrived vanished at the shock of an overly excited nearly-adult pony racing toward her. As Pinkie Pie hopped about Luna looked overwhelmingly confused.
Twilight was stunned for a moment. Did Pinkie Pie not realize that she needed to treat royalty with respect? That Princess Luna was too socially awkward and inept to be rushed and assaulted by such spectacular displays of friendship? In her haste to "rescue" the princess she hurried over and virtually tackled Pinkie Pie to stop her harassing the princess. She skidded to a stop as her body knocked into Pinkie Pie's hard enough to send her flying to the floor. She smiled apologetically at Luna while Rainbow Dash's uncontrollable laughter echoed in the vast hall. Pinkie Pie's giggles soon sounded from the floor as well. Before long Rainbow Dash and Pinkie were supporting each other back-to-back while howling with laughter.
Twiligth Sparkle was speechless with mortification and nervousness; but Princess Luna merely looked upon the two with an eyebrow raised. She knew these ponies had a clear understanding of what the word 'fun' meant; but she couldn't see how rolling on the ground and squealing or howling could possibly bring any remarkable amount of enjoyment.
"Princess, please excuse my friends, they don't mean to disrespect your highness."
"This is quite alright Twilight Sparkle; we are here to have fun and to become friends. If this is the behavior friends partake in than I shall partake as well. Also, I believe I told you on Nightmare Night to call me Luna."
"Yay! We are going to have so much fun!" Pinkie Pie shouted, once again hopping in a dizzying circle around Luna. The princess's eyes followed her movements spastically, she smiled and was clearly trying to match Pinkie Pie's signature impossible smile exactly. It made her look a tad deranged and she heard Rainbow Dash snortling off to the side, Rarity and Applejack were obviously having great difficulty keeping their laughter at bay.
She saw Fluttershy still cowering behind Applejack and looking skeptically at Luna. This would be a long night.
"Yes. Well shall we...move on to the great hall, then?" Luna suggested, still somewhat hypnotized by Pinkie Pie's endless energy.
They made their way to the great hall, with Pinkie Pie hopping the whole way and Rainbow Dash frequently flying ahead of them and circling back in impatience. Twilight watched as Luna's eyes shifted between dancing to Pinkie's movements and glancing at Rainbow Dash above. She couldn't tell what the princess was thinking about her friends, her face was as aristocratically stoic as ever.
But still, she wished there was some way to inconspicuously communicate to Rainbow Dash about her rudeness, not that the hardheaded pegasus would listen of course—nor would Pinkie for that matter.
When they finally arrived, the girls observed that the room was done up nicely for a party. They all thought that clearly Princess Celestia had decorated the room, or at the very least directed its design. If it were up to Luna, surely the hall would resemble what it would have looked like way back before Luna became Nightmare Moon—like some snooty theme party.
Nonetheless, the hall, as large as it was, was filled with glitter and streamers in many colors. There were fancy desserts and colorful drinks on a large table off to the side, and plump sparkling pillows large enough for three ponies to sleep on were scattered about.
Everyone thought it was all a bit much; everyone except Pinkie Pie of course who was desperately wanting to dance around the entire large room and watch the glitter swirl.
Princess Luna sat down on a ridiculously large and plush royal purple pillow. She sat and stared expectantly at her guests. Rainbow Dash dived unto another overstuffed pillow and landed into the dense fluff with a wonderfully comical 'puh'. This caused her friends to laugh heartily; even Luna smiled. She then lounged back as if on one of her clouds and her friends began to show off their own varying ways of diving unto the many plush pillows about the room.
Rarity stood up on two legs and threw an arm over her eyes, dramatically swooning on to her pillow. Applejack ran fast towards one and back flipped on to it, earning a mimed hat-tipping from Rainbow Dash; Pinkie Pie pirouetted before leaping artistically unto Rainbow Dash's pillow, getting a playful glare from the lounging pony. Fluttershy studied the cushion nearest to her before stepping on to it normally; this earned the biggest laugh from the girls. Princess Luna studied the scene studiously, then she flew straight up and laid backwards in the air, allowing herself to fall flat on her back into the cushion. The girls giggled and cheered for her, even Twilight seemed to loosen up a bit more and smiled at the princess before pretending to trip unto Fluttershy's pillow.
The princess popped up once more from the pillow, her dark ghostly hair flung forward to hang over her face. "What fun that was, we must do more!" She said excitedly.
"You bet," said Rainbow Dash flying up and 'puh'ing on to another pillow. "These things are the best!"
"I say we eat cake!" Pinkie shouted from the table where she had already eaten half of a large cake. "Or I know, we could do both!" Pinkie Pie hopped up with a battle cry and smashed into the half-cake like a cannonball.
For the record I love Pinkie Pie's voice.