If your fiance had vacation time than she is entitled to take it as long as she provided the requisite notice. If she had no time and needed it anyway I cannot say she is entitled but it is very rare that she would be denied for medical purposes. She should look at her employment contract for an caveats on this issue than I advise calling a local employment lawyer.You usually can get a free consultation and in doing so will learn the specifics regarding your case. From what you have said she did not act unreasonably however I do not know the specifics of time needed or notice. She should definitely consult an attorney if she was in fact fired to make sure it was valid per her employment contract