Hello lucyinthesky Like some others who have posted, I do not think you should feel bad about having tried to prepare your daughter for a future without you some day. This is sensible thinking - and which is at the root of most supported housing provision for people assessed to be vulnerable.In many cases it is a statutory duty for local authorities (housing and social services, which should work together) to provide this, depending on the level of need. Any assessment from the mental health team should look at how people manage (or not) at their worst, not just on a good day.
Your daughter has done brilliantly to get and keep the job she has in an area where there is so much competition. However, she has a right to want to live independently of you, whatever her health problems are - and you to want this for her.
You could both benefit from getting some housing advice/assistance from your local council housing advice centre. There are in many areas (affordable, rented) independent living flats designed especially for young/youngish! people with mental health problems who can work but still need a bit of support from time to time. AND where, if things go pear shaped, they do not become homeless, as their rent can still be covered by housing benefit.Provision varies - and it may not be available immediately. Also,you will need letters of support at some point from doctors etc and the mental health team.
I have friends whose adult daughter is now in this situation, and though it took time and a lot of courage for her to leave the parental home, she did -and it is working out really well (as is her career and her friendships). Mum and Dad live within half an hour's journey so it is easy to maintain contact, and they do not have to worry nearly so much now about how things will be for her when they are no longer around. Take care, and hope things work out for you both x.