✔ 最佳答案
Your word against hers. And if you took him to the vet since having him and bought supplies for him, etc. then she's SOL. You have solid proof that is YOUR dog. Save text messages, emails, etc. concerning him as well.
Papers mean nothing. I wouldn't even bother with them. But get your proof together, from pictures with dates on them to vet receipts, etc. and make sure he's microchipped and registered in your name, too.
Oh, and get him neutered ASAP. Chances are good she's decided that (even w/out knowing his lineage, history, etc.) the twit has decided to BREED him. If you neuter him, there's a good chance she stops asking!