I know this is going to hurt my friends’ feelings,
Well, it may or it may not destroy or hurt your friendship.
Part of that may be how clear it was while in college that you were Catholic. And I din’t mean preaching, but rather how you lived your life while at school, and with them. As I noted above, I had a co-worker do the same, and while I don’t go around providing constant commentary that I am Catholic, she knew I was…
Gays, like everyone else, have information and opinions. Some expect that whatever “faith” one has will be a private personal thing and not get in the way of “friendship”. Others have pushed the edge, rather than just wanting to be “accepted”, they now are out to prove a point by challenging those who have a faith which indicates that homosexual activity is immoral.
And others understand that one can be friends, even close friends, in spite of different approaches to the issue of gay marriage.
It is possible you may not be invited, if she understands that presents a conflict to you.
Or she may be oblivious to the conflict, and presume your faith would not create a conflict. There are two alternatives above - not available, or a polite answer as per HomeschoolDad.
Or there may be a third, that she makes this a litmus test of what she perceives as friendship, and you may lose a friend. That may or may not be permanent, and it may or may not splash over onto any of the rest of the circle who decide to take sides.
Should the last occur, then you may have found a real world example of the fact that people have many acquaintances with whom they share a lot, and few friends - those who accept us as we are, not as they want us to be. And we often confuse the two.
That last is a hard lesson, part of growing in life experience and in faith as an adult.
As to the other women in the group, I would not recommend discussing it much unless they bring it up.