as Jorats said, she needs to see a vet immediately so that she can be put on the proper medication.
It could be an inner ear infection, she may have fallen, or it could be something else.
Does she seem weaker on one side then the other, does she have a head tilt (as Jorats asked), is she walking in circles?
If she has an inner ear infection, she will need an antibiotic or combo of antibiotics plus an anti-inflammatory to try to prevent permanent damage. If she is on meds and after a few days she is getting worse or they do not seem to be helping, then she probably needs different medication so she will need to see the vet and get different meds. Inner ear infections take at least 6 weeks to several months to be completely treated. Untreated inner ear infections will kill.
She will likely need modifications to the cage to make sure it is safe for her.
You will need to hand feed her soft foods as she likely has trouble eating ....... foods such as rat blocks soaked in cool water to make mush, baby food, cooked and mashed sweet potato, organic soy infant formula thickened with a bit of baby cereal etc.
You will need to make sure that she gets enough to eat and most importantly that she is well hydrated as dehydration kills. A water dish that can not be upset may help as she may be unable to use a water bottle
You may also need to help her stay groomed if she is unable to do it herself.
Her rattie friends will likely help her and comfort her.
A low house, or box used as a house may help her be able to stay upright by helping her to know where up and down are
Here is some info
http://ratguide.com/health/auricle_ear/otitis_media_otitis_interna_labyrinthitis.php
Please let us know what the vet says and how she is doing