Have her sit on the edge of a chair and stand up and sit down
Then have her stand up and squat and stand up
OR have her lower down only as far as she can with her heels down, once they come up, have her stop her squat
Personally, I don’t use squats for overweight clients. I feel it’s too awkward and can be irritating to the knee joint, especially if the are doing them incorrectley.
Wall sits are a good alternative.