She may not be terminated for being sick, or for having used FMLA. She may be terminated for a legitimate, non-illness and non-FMLA reason, such as:1) Downsizing or restructuring due to provable economic issues (e.g. she is a money-losing operation or department).2) Documented and provable performance issues.3) Provable absenteeism, chronic lateness, insubordination, criminal acts at work, violation of company policy or superviser instructions, etc. But if she is let go and there is no provable other reason, then this may be because she has a medical condition or as retaliation for using FMLA, and either is illegal. If she thinks this is the case, she should contact the EEOC about filing a complaint.