Late twenties? long term boyfriend??
I think your folks are still treating her like a child.
I was sixteen when my parents let me have my boyfriend stay. I had a very open and honest relationship with them and they realised 'it' was going to happen anyway, may as well be in the safe environment of home.
He ended up moving in with us so we could save for a deposit on our first home. At 20 years old we were home owners.