You should consider assisted living when the care needed by the elder starts becoming closer to 24/7. As we age - there comes a point in time where we become like toddlers. We need a safe & elder-proofed environment. We need eyes on us 24/7. And one family or one set of family members usually doesn't have the ability (sleep loss is real) or the skill (how do you help up an elder that's fallen without putting out your own back?) to do an adequate job of it. The kindest, most caring thing we can do is to provide for the safety of someone we love. If your mother-in-law falls & ends up in the hospital - it'll be way more expensive on all levels than the cost of preventative care. Good luck!