Wife is worried of getting job eliminated while on maternity/fmla since they are hiring replacement, what are her options beside resigning on her own?

If she was granted FMLA and she returns to work within the 12 period that the employer granted her under the FMLA, then the company cannot simply replace her.  Rather, the FMLA requires that they return her to her job or a very similar position.  If she is not able to return to work within the FMLA period that was granted, then her situation gets more complicated.   In either event, I see no reason for her to resign. If, however, the company was legitimately planning to eliminate her or her job even had she not gone on FMLA, the company could do so without violating her rights.  BUT, the company would have to prove they were truly going to terminate or replace her and had this intent before she ever asked for FMLA and perhaps before she told them she was pregnant. Regardless of the situation, she should definitely discuss this in more detail with an attorney to explore all the facts and other possible legal action