When an employee is on FMLA leave, an employer may make periodic inquiries about an employee's status and intention to return to work. If the employee said that she was going to return to work, and the employer responded by suggesting that she resign, that may raise questions. If the employee said that she was not certain, and the employer offered to give her priority for rehire if she decided not to return to work, that might give her an incentive to decline to return to work but is not inherently improper.
If she declines to return to work due to her being disabled from working, then she will not be able to get unemployment, as you must be able to work to collect unemployment. If she remains disabled beyond the end of her FMLA leave, she should seek disability benefits (private disability insurance if she has it, state disability if she's in a state such as California, or Social Security disability benefits).
If she is able to work at the end of her leave, with or without reasonable accommodation consistent with her rights under the Americans with Disabilities Act (ADA), but her employer won't accommodate her or allow her to return, the request that she resign would tie into a larger argument that they are engaged in disability discrimination.

