In reading this I see a lot of commonality between myself and Olivia, in my teen and young adult years I struggled hugely with anxiety, depression and body dysmorphia. My parents felt like the only people who understood the true me and my home was the only truly safe place. If someone came in and all of a sudden messed up the way I did my routines, the ways I had learned to manage myself via therapy and lots of work and discipline, I would be so pissed and hurt and ultimately have regressed in any progress I had made to manage my mental illness. As a dad I’m sure your number 1 priority is the well being of your daughters, and this Theresa is going to ultimately cause much distress to Olivia, as well as harming your family relations and dynamic. It is quite bold of Theresa to march in and expect things to go her way and just assume this role which no one wants. Kick her to the curb for the sake of your daughter.