My DD and her partner chose to live with me about 15/20 years ago when they were in their late30s/early 40s.
So, yes we are very close. It helps that the house is quite large and we each have our own living rooms, so we're not on top of each other.
The other thing that has helped is I see her as an adult person, capable and sensible. I dont interfere or give any opinion on her primary relationship with her partner. We all have an equal say in what happens in the house, (decor in joint areas etc)
Apart from thst, she's always been good company, makes me laugh. We are both interested in the same things, but can have different opinions on some. I respect her opinions, she respects mine.
As well as always loving her, I've always liked her too. Her teenage years were a tad bumpy, but not too bad. One example of her ways to make me laugh, she once said, when a teenager, don't worry mum, it's just a phase I'm going through. Very self aware woman, is my daughter.