It is okay for a child to cry. Crying is her way of telling you she wants her own way even though you are insisting that she does what is best for her. If she wanted to play in the street and cried for hours when you brought her back into the yard, you would not give in to her demands and let her play in the street.
She is a little kid and she wants what she wants, and she has now learned that if she screams and cries you will give her anything she wants in order to have peace and quiet.
As parents we have to get past the guilty feelings of saying "no" to our children, and get past the fear of hearing them cry. We know what is best for them, whether they think it is a good thing or not!!
It would be good to mention to her throughout the day, just a comment from time to time, how wonderful it is that she has her own bed to sleep in and her own room; also, going in and looking at the bed and admiring it as a fun wonderful place to be at night... and talk about how fun it will be tonight to sleep the whole night in her own bed... things like that, so you are building it up to be a wonderful fun experience. Then as it gets closer to bed time, maybe right after dinner during her bath, chat in a happy upbeat way that tonight she gets to sleep in her own bed like a big girl, and if she wakes up and forgets that she's staying in her own bed tonight that's okay because you will be happy to take her back in her own bed, won't that be fun!!!!
The important thing is that you stay upbeat and positive and make it a fun fun happy thing. No "or else" or "you better not get up" or stuff like that.
The other very important thing is your consistency. If you relent even ONCE then she will never believe you again. It is very important that each time she gets up at night you have a calm demeanor as you immediately walk her back to her room and help her climb into her bed. I wouldn't carry her, unless she is throwing a tantrum ;-) but you are trying to encourage her to grow up beyond infancy, which includes being able to walk on her own and being able to climb into her own bed "like a big girl."
Remember that she is not crying because the bed is hurting her, or because it is cruel and unusual punishment for you her mom to expect her to sleep in her own bed. She is crying because it works: it makes you give her what she wants. The way to stop the crying is to stop giving her what she wants based on the loudness and intensity of her crying -- instead, give her what she wants based on her proper method of asking for it (and of course her best interests as you see it).
Also, make sure she is not drinking water before bedtime else she will awaken to use the bathroom; if she continues to refuse to go to sleep then cut out her afternoon nap so that she will fall asleep out of sheer exhaustion!!
Another thing that helps is a bedtime ritual, such as bathtime, snuggle time, read a short book in her bed, lights out, pray, sing a song, and "good night, have a good sleep, I will see you in the morning." This is what I did with my kids and my granddaughter, and bedtime was never an issue no matter where we were (you know how strange beds are not as easy to sleep in, especially for kids).