Right away. But do not leave her out with access to the furniture if she isn't trained that way. Better to have an area puppy proofed for her to be in while you are not right there, and use an extra tall baby gate to keep her in there, then teach her about the rest of the house while you are there. For now.
If she said 90% house trained, don't count on it. If she is still having accidents at the woman's house, she isn't house trained. And she will need a good schedule and lots of praise for going where she ought to. A bell hanging on the door you take her out of can come in handy as well. She will here it ringing every time you take her out, and one day you will here it ringing, and there she will be ready and needing to go out. Good girl.
Good luck with the puppy.
Heidi Ho, Odie
Joy-Joy, Bear Cub, Hepsi-Pepsi
Cujo2, Karma Chameleon
Ramona the Pest, Kojak -- who loves you baby?
Tiny Tinnie, Susie's Uzzi, Kaiah -- The Baby Monster.