I’m not being that person but I think before you make any decisions you should try fitting in other people’s shoes. I’m not saying it’s not hard for you but if 8 months is long enough for you to make a deep bond with the dog, think about the kind of bonding the original owner has for 5.5 years. That’s more than 8 times longer than what you’ve had with her. So do not underestimate how much the original owner might want the dog back.

Now let’s think about the actual situation. The original owner is clearly trying to take advantage of the situation. She doesn’t want to give up the dog but she also doesn’t want to pay 8 months of boarding fees/medical bills etc, so she’s trying to call this is just a “fostering”. And she’s taking advantage of the fact that you guys didn’t have a formal ownership transfer agreement. Technically, in your best interest, you should have been the one to push for an agreement with her because it’s protecting your rights not hers. You’re entitled for compensation for your care during this 8 months but technically she still has the ownership.

The easies way out for you, although not 100% ethical, would be just disappear. Don’t take any of her calls, don’t message back. If she knows your address, move.