Of course she would wind up in a random hotel with no one around. This sort of stuff happened to Donna Noble all the time, ever since she met that Doctor. She'd been nearly killed, had her emotions toyed with, and seen more than any human was ever meant to see.
And she loved every second of it.
Donna of course, was easily annoyed with her best friend, and he was with her, but the two loved each other to an extent that the two couldn't stand time and space without each other. He got a companion, and she got the times of her life.
So she wandered through the hotel alone, looking for the 'Spaceman.'
"Oi, if you think you can leave me here alone, Mr. Martian, I will rip both your hearts out and eat them in front of you!" she yelled towards nothing. Her voice merely echoed down the halls, so she continued to wander. But when she listened closely to the echoes, she thought for a second that some of them were not her own.
Then she found the door.
She decided to open it, just knowing she had to. And when she did, she regretted it immediately.
She was standing there, in front of herself. The Donna that she was looking at talked on the phone to one of her friends, ignoring the Donna that just walked in.
"…and then of course that Daniel bastard had to ruin everything at the party. Stephanie tried kicking him out but he just wandered around drunk and flirted with Daphne- hold on, someone's on the other line."
The other Donna pressed a button on her phone and began talking to the stranger. "No, I'm not sure who that is, sorry… Well if you could be specific as to which doctor you were talking about I could answer, but I don't know anyone named 'the Doctor.' You a druggy or something? Ugh, look for dealers elsewhere, please."
Donna hung up the phone, and the real Donna waved her hand in front of her, finally seeming to get her attention.
"Oh, of course," said the other Donna. "I'm dreaming. I mean, there's me standing in front of me, and only in a nightmare would I stay somewhere so tacky."
"What do you mean you don't know the Doctor?"
"I don't know who that is, sorry. You a druggy too?"
"The Doctor. Your wedding day, the Rachnos, Pompei, Agatha Christie?"
"Iphones, Klingons, and JK Rowling. Alright, now you name some random gibberish, dream me."
"I'm serious, dream me! You don't know who the Doctor is?" Donna was beginning to feel dizzy when the other her insisted that she'd never known anyone named the Doctor.
Donna waltzed out of the room, feeling horrible. She continued to walk the halls, wondering what had just happened. She heard the TARDIS noise off the in the distance after an hour, and was extremely relieved. She ran in the direction of the sound, knowing fully who the Doctor was.
She found the Doctor, in his trench coat and with his funny hair, standing in the lobby, awaiting her.
"Donna!"
"Spaceman! What happened?"
The Doctor proceeded to get his sonic screwdriver from his pocket, and Donna knew what this meant. He was going to activate some device to find their way out of there or something.
Instead, he smacked her on the head with it.
"Ow!" After a moment of pain, she found herself lying in the TARDIS. The Doctor stood over her smiling. "You're back!"
Slap!
"Ouch! What was that for!?"
"You hit me in a dream!"
"That wasn't a dream Donna, that was a place of fear."
"What?"
"This place, it's been snatching the minds of people and putting them in there to experience their worst fears."
"Doctor, I thought I heard other people in there."
"Don't worry, we're going to the fourteenth planet of the Yinubelt System to find out how. There's plenty of spare parts lying around to make something, so that way I can stay there longer rather than a few seconds, and get everyone out of there."
"What, by smacking them on the heads?"
"Probably."
"Wait, lying around? Like a junkyard?"
"Yeah, well, it is the dumping site for the entire Andromeda Galaxy, so…"
"Oi then, I'll stay here in the TARDIS while you go scrapping around through alien-dog crap and broken future toilets."
"Alright, just let me set a course. And you're coming whether you like it or not."
"Why?"
"Revenge for your revenge. Besides, the only reason I hit you on the head was to save you."
As the TARDIS flew through the time vortex, Donna thought over her experience, and she figured out what her worst fear was.
Her worst fear was a life without the Doctor. A life of not knowing him, with no memory or experience of the amazing things that she'd seen.
That's why she was going to travel with this man forever. That was her master plan, at least.