So sorry to hear that grown ups sometimes act like middle schoolers! As a recently retired MS counselor, I have to say that sometimes "mean girls" come in all ages, and the best way to deal with them is to avoid them. But that being said, I also advise that if your guild has sew days, classes, community service activities--get involved and don't wait for a personal invite--the announcement in the meetings & newsletters is the invite for all--no one gets a personal invite. Sure it's hard to show up by yourself the first couple of times--but after that I'm guessing you won't feel so new. Also--volunteer to serve on committees--in the Guild I belong to, we are always asking for help, and while it's true that long time members are often the ones asked to do the job, it' usually because that person's availability is known already.
And it's wise to enforce the wearing of name tags unless the group is under 20!