Do you get along with the GM? Have you explained your feelings about the situation? Would be good if the GM could see it from a logical view, that Zoe would be much more suited and happier in a lifestyle where she gets attention, care and love from your home that she is obviously not getting from the wicked witch, I mean the lady (supposed owner).
I know it’s not up to the GM to choose the better owner, but if he understood the situation and saw the opportunity to help Zoe, then he could tell the lady that she has to show in such and such a time and stop extending the contract.
ETA: I saw the GM knows your feelings… tough situation. Make sure *if the lady comes back, she knows that she doesn’t have to keep Zoe if it is too much for her, as it seems to be. That Zoe will go to a good replacement home.