Her condition, commonly referred to as "wry neck" could be caused by a number of things, but the most likely cause is an inner ear infection. She will need to be seen by your vet to determine whether or not her eardrum is still intact and to decide upon the proper course of treatment. If the cause is an infection, she definitely will need to be treated with antibiotics from your vet, but he may also prescribe an ear drop which contains both a topical antibiotic and an anti-inflammatory drug.
In most cases with this treatment, it only takes a few days for a rat to get its balance back, but the treatment must be continued for at least one to two weeks.
Another possible cause of head tilt can be a pituitary tumor, which is more common in older female rats, but can be seen in younger rats and even in male rats. There is no treatment for this condition that will cure it, however, anti-inflammatory drugs, such as Prednisone or Dexamethasone, may reduce the swelling slightly and prolong the life of the rat for a short time. Spaying female rats is said to reduce the risk of pituitary tumors, but it is still no guarantee.
A stroke is another possibility. Again, it would be more common in older rats, but it’s not impossible for a younger rat to have a stroke. Anti- inflammatory drugs may help in this situation, too, but for the most part, only time will tell if the damage is permanent or not. In many cases, a full recovery from a stroke can be made in a short period of time (a few days to a week).