It is important to make sure there are no physical concerns that could be contributing to her behavior. In girls especially, urinary tract (bladder and kidney) infections can cause children to have accidents. The typical symptoms of burning or pain with urination may not be present. Similarly, diabetes can cause a young child to have more frequent urination, and thus contribute to more accidents. You should talk with your doctor about whether your daughter needs to be evaluated further.
Remember also that two- and three-year-olds are struggling with the issues of control and independence, and toileting is one thing that they truly do have control over. If there are no signs of any sort of medical problem, you will have to be patient and help her to relearn her potty skills. I suggest giving her control of some other aspects of her life (what clothes to put on, which story to read, which sandwich to eat for lunch, etc.), and you may find that she has less of a need to demonstrate her control over where she pees.