Afraid I have waited too long

[MrBond]

"She says she would need a signed agreement that would then carry through to the D."

Tell her 'no'. Tell her that you are not going to sign anything that you are not comfortable with. That you will be moving into the side room and she is more than welcome to do what she feels like to do.

"My problem is how to tell her I am moving back in the least upsetting way so it doesn't turn into an ugly argument."

See above.