I think it's a case where leading by example is most helpful. A lot of the tumblr types who are using WLW and Queer etc. - It's all they know. It's not much good trying to argue with them, because a lot of them have a very limited and skewed perspective on the history of the LGB movement.

Being able to SEE the alternative in action is when the penny seems to drop for a lot of them.

So - use the word lesbian. Explain why you choose to use that word, over other words. Support those groups that are about re-claiming lesbianism for lesbians, like Get the L Out, or the new LGB group that's started up in the UK (which is very clear about the need to specifically support lesbians in particular because of the QT stuff).

If you're going to start a group - even just a small group that's just for a few friends, people you know or whatever - then be clear. It's lesbian only. If someone comes along who is bi, or queer, or WLW, and wants in, say no, it's for lesbians, and send them on their way.

Make it clear that all those other groups are not lesbians, and do not represent lesbians, as far as you are concerned. Don't enable your own erasure when you can help it.