It's really hard to say, I know that different T's may all feel differently about bounderies, but I think something like this, Is not really teetering on a boundary. You not going to friend your T, but I understand the concern that you are worried that the T will un-friend this person. Can you hold off friending this person until you talk to your T and be upfront about it? Just maybe send this person an email or even get her thoughts on it. Just tell her, that you noticed your T is on her list and you want to talk to your T first? I don't think it would be fair for you not to be able to friend this woman and I don't think it would be fair for your T to unfriend because of this. I just think its best to let this woman know that you need to tell your T first, as to avoid any conflict.