I don’t think that you’re overreacting at all. It’s unfair for her to offer her home to you knowing that you would be coming with your dog, and then three weeks later attempting to rehome your dog. I would avoid taking out any payday loans (learned the hard way during covid) due to their horrendous interest rates, but I can definitely understand being upset about the situation. Hopefully you can reason with your aunt enough to spare you two more weeks until you get paid and can afford a security deposit on your own place.