Legal Question in Wills and Trusts in Florida

No, but you can get her a guardian and/or conservator.

The problem is not the living will, its that she is mentally unable to appoint. A Power of Attorney isn't valid unless the maker of it is legally competent.

The alternative now is a guardianship.

Unfortunately not, as stated above. Competency is required to execute any type of estate planning document. However, guardianship is your next option to accomplish your objectives.