How do I not be friends with the kid's mother?

Okay our daughter played with a nice girl around the corner. But the mother seems nutty! She does not stop talking. She's very eratic and I can tell has issues. We met her for the first time today and she is already asking us if we want to do this and that. My husband and I are kind of weary of her. I am not looking for a new friend. How can we avoid becoming "friends" with her yet still have our children be friends and have play dates? They live very close to us.