Hi I was wondering if someone can help me.

Here's the problem my dog had puppies and a lady called me intrested in a puppy and I said I would sell her one if she sent me a adoption agreement and a 200 deposit well in the mean time I I said she could have it but I never received the adoption agreement or the deposit and got nervouce that she would never by the puppy so well I had another buyer came and gave me a deposit and I sold it to them and apologized to her and told her it was because I never saw the adoption agreement or the deposit she is claiming that she will take legal terms and sue me for all her lawyer fees and that she will bad mouth me to akc and make so I will not be able to register my puppies through akc in the future what do I do and can she do this

You had no contract with her. You accepted no money. Tough luck for her. If you gave her ample time that is all you can do... why not offer her another pup! She has sour grapes!