[Brat]

She probably walks away from these conversations thinking she's educating YOU, and thinks she's relating to you better by talking about an issue that is near and dear to your heart. To her, it is probably just making conversation.

These are all just my uneducated guesses, especially since I don't know this lady. But the next time you see her, what do you think about just expecting her to say something negative about adoption? Then, because you aren't caught off guard when she does, you can take a deep breath and approach her differently. Instead of trying to educate her, "innocently" ask her probing questions about what she has just said, as though she knows it all. If she's trying to bother you, perhaps it will show her that you're not going to clam up and get frustrated. If she's completely innocent in her comments, the tone of her responses may indicate that she's teachable, and you'll be calm enough after that deep breath to speak gently to her about the truths of adoption.

I love my daughter so much, and I take it very personally when people make comments about adoption, because I want her to live in a world where people understand her. But I'm realizing that I can completely eradicate adoptism as much as I can eradicate racism for her sake. That takes the pressure off so I can pick my battles--as the other posters mentioned--as well as think strategically when someone becomes an on-going problem that needs to be addressed for my own sanity.

Hang in there.