I truly hope this comment has been seen, a few good trusted friends that would honor op’s memory by taking care of good usage of his daughter resources is the safest way to go, by far
My parents set up a trust for my disabled brother and made my uncle the guardian. Unfortunately he was dishonest and greedy and embezzled it. Fortunately he did this before my parents had even passed, so we had time to come up with a backup plan. (The backup plan was me, and I never felt like I could start my own family as long as I was responsible for my brother, so ... that's been limiting.) Anyway...
... I've often felt like it would have been much safer to either make a legal firm administrators of the fund or at least have multiple family members on it, so that they might keep tabs on each other and make it harder to just steal. I've actually spent a lot of time thinking about what went wrong and what might have been different. If that uncle hadn't died I would probably have spent that time fantasizing about ways to kill him, but, as it is ... I just don't get to retire.
I love my brother and have made peace with most of the consequences of what happened to him, because at a certain point you just have to accept the hand you're dealt and keep going. But the bitterness of what the world has done to us is still in me and I don't think it's ever going to leave.
tl;dr - definitely don't leave just one person, even family, with access to a disabled person's money
(To be clear, I was trying to elaborate on your point and not disagree with it.)
I wish there were better legal resources for the parents of disabled children to do this in the US. Like the original comment pointed out, the legal expenses of setting up a trust are steep, and if you're already fighting an uphill battle with medical costs it can be impractical. Or even totally out of reach.