I would just tell nicely that you could not do that as you need it for your own personal safety. Generally they are fitted for your height. She should have one of her own. There are agencies that would help the daughter get one for her Mom. Generally after knee surgery you already have a walker...
My Bro had a Cherry Bomb go off in his hand. Lots of damage to his hand and fragments to his leg. He was so lucky in many ways and his hand is now useable.
A few years ago there was a big scam in the midwest and got quite a few Seniors. Fed them big meals and alot of high pressure talks. For every thousand you give us, we can make you five thousand. Let us manage your securities, savings etc and we can make you so much more than you are now...
Maybe explained to your daughter in law of your restrictions. Though we don't like to, maybe you should consider telling your family you have a few health issues and have to be careful what you eat. I have eating issues, have told my kids and have asked them to fix what ever they were going to...