Quoting Heeeeeey, Sexy lady. ;):" I'm trying to avoid it. I just don't really know how to reply when she asks me stuff about him. Like ... [snip!] ... asking me for her name and I kept telling her I don't know. I've never seen her or talked to her. I don't think she bought it."
Just be honest, tell her your happy to chat and keep in touch etc but as far as he goes etc you would rather not discuss it and tell her its not to be mean you just dont want to get in the middle or upset and lose either of them. Trust me you will no matter how good your intentions are it will fire back on you iv had it happen. Just tell her straight up that anything to do with him she needs to talk to him directly etc