Your cat is scared, obviously, and will come out when she gets used to her new home.
The first thing to do now is to get her some food. Take some wet food on a plate (you might add a couple of spoons of water to the food), push this under the bed, then walk away so she can eat alone.
If the cat stays under the bed for more than 2-3 days, it is time to make it come out. Reach your hand behind the cat and gently make the cat move out of her hiding place. When the cat is out, pet her for a short time before letting her go. And don't do so until 2-3 days have passed.
You can also make or get some small toys and try to get her to play with them to make your cat forget that she is scared for a moment while she is playing.
Your cat feels safe under the bed for now, but you have to make the cat feel safe in all the other places in your home too.
Your cat might have had an accident under the bed and this must be cleaned up.
The first couple of days in a new place can be stressful for a little cat, so you must try to comfort her as best you can.