Employment Law Questions? Ask an Employment Lawyer.
I am sorry to hear about your situation. The seems very unethical on the part of your employer. You may have a very strong legal claim for wrongful termination in that they seem to be firing you because you're about to use her FMLA privileges. I would suggest contacting a local employment attorney to try to negotiate some arrangement with them or else you will file a lawsuit.
If you have any additional questions just let me know otherwise a positive rating would be greatly appreciated.