No one recognizes a saint at their own hearth.
When we live with someone, no matter how much we love them or how close we are with them... there are frictions. When it's a multigenerational house (grandparents, parents, children/grandchildren... it becomes far far more full of friction.
Dozens of cultures practice multigenerational living. Nearly all have a top down hierarchy. Elders first, parents second, children third.
Psychologically... this is what happens even in our culture. We fall into old roles/ scripts/ schema's.
You want an adult relationship with your daughter... she'll need to be secure in her own adulthood to be able to do that. Seems like when she moved back in with you guys... she lost a lot of her identity. She's relating to you like a child, but still has the responsibilities of a parent and an adult. Been there, done that. With the best mum in the world, with the best intentions in the world, after years of being on my own -fully capable-, and yet. And, yet. And YET... in my mother's house I'm only an adult when I'm visiting. Even then, it's VERY easy for us to fall back into the same roles we held for 17 years. She bends over backwards not to 'parent' my son / her grandson. She still does. Every time I wear metaphorical steel toed boots (because my toes get stepped on a LOT). And she's not even meaning to usurp "my" job/role.
Her house, her rules, her schedule. Yes. We had our own space. But when you share a house with anyone, you're not autonomous. Even with the best relationship before sharing... it can become a huge stressor. But in pieces. Bit by bit over time, sooooo gradually that the players don't even notice what they're doing.
I haven't lived with my mum (one of my best friends) for years and years. I left home at 17, moved back in for about 6 months about 10 years later (with my husband and toddler), and have been out, ever since. I haven't kept a 'messy' living space since I was a teenager. Heck, when I lived there my parents were constantly raving about my 'normal' cleaning up. And tonight at a family dinner... I was being teased about how messy I am.
Say what? I sweep and mop every day, wash sheets and towels once a week, wash my walls/curtains/comforters every 3 months. Is my house spotless? No. But I am a very clean person. I NEED clear and open space that is organized in order to be able to think clearly. My sister who was there with us just cracked up and died laughing. My parents were thinking of me 20 years ago. Not how I am now.
And how did I react to the teasing? How I would have 20 years ago.
Schemas.
I'm VERY close with my mum. She's one of my best friends. BUT we need our space from each other in order to maintain an adult relationship. And even then, it backslides from time to time.
As an example you've given... you've told her NUMEROUS times that come Sept1 you'll be moving into a smaller place with just your husband.
Dear. God. Why?
If your daughter isn't mentally deficient... she heard you the first time, and has probably been exploring various options. But you keep reminding her. As if she's a child (10 minutes till time to leave, 5 minutes till time to leave, 3 minutes, are you getting ready? 2 minutes. You'd better be getting ready. It's time to go! Are you ready?? C'mon, are you ready?) This kind of micromanaging just becomes a kneejerk reaction with parents and kids... and it inevitably drives adults insane. They don't want to be constantly reminded, grilled, having their choices judged or put down (that will never work / really? / have you really been blah blah blah). By and large people react 1 of 2 ways: shutting down and refusing to discuss it, or a screaming match.
2 more months. In 2 more months yuo'll each have your own space. Keep in touch on a regular basis... but also give it TIME for your relationship to get back on equal and adult footing.
Right now, it's ALMOST impossible for either of you to recognize the saint at your hearth. She you, or you her. You were close before. You've undoubtedly grown closer/shared good times in many ways over the past 2 years, but are dealing with a lot of friction right now. You'll be close again. You two just need a little space.