bought a dog.

We bought a 4yo dog 8 months ago for $200. Over a month ago I found out I was pregnant and started to have a severe allergic reaction to said dog. After quite the process, we found a wonderful family who instantly fell in love with him. So we adopted him out to them. The previous owner (who we got him from) has been harassing me nonstop. Threatening to come on base and talk to authorities. I've spoken to her about it and she's accusing me of lying (which I haven't). In our "agreement" 8 months ago, I was to let her know if anything were to happen to where we couldn't keep him, apparently. She wants their phone number, which I can't just give out for legal reasons. She said he was microchipped and everything, which he wasn't. So we had that done when we got him. Among other things. I understand where she's coming from but I've spoken to her about him being with a new family down the road and upon us purchasing the dog from her, he was then our responsibility. What do I do?! I'm so stressed out. She's saying there's a "text agreement" and that she has all of the texts from back then. Nothing was signed.