I am a straight, married female, mid 40's, I have a great neighbor, she is a really nice person and I enjoy her company,she is also a lesbian. This is totally OK with me as her sexual preferences are none of my business.
The problem is that when she comes over to visit she starts making unwanted sexual advances towards me and my other straight friends. I have tried to be kind in the way I tell her that this is not acceptable behavior with me but it does not seem to be working.
How do I get her to stop this without being mean or hurtful?

When the two of you are alone and talking, and she says something that causes you discomfort, say, "stop it." Remind her that you have asked her to stop it before. She probably doesn't realize how often she is doing it or how uncomfortable it is making you. Tell her to stop it as many times as it takes. She will.

How would you deal with a man that did you that way?
If it were me and it happened more than once I would really get pi$$y... I would also get pi$$y if a man did not honor my request. There would be no friendship... it is hard to be friends with someone that will continue to disregard your feelings.

If you do want the friendship of this woman, but not the advances, try explaining it to her that way. For example, "I enjoy having you as a friend, but I don't want the friendship if you continue making me (and my friends) uncomfortable." If she values your friendship, she will stop. If she continues, tell her that you are not only ending the friendship, but filing sexual harassment charges against her (even if you're not). You have plenty of witnessess in your other friends.
If she is in need of serious therapy, a restraining order may be necessary, as well.

If she does not respect your wishes than I do not see how it is a true friendship... I would keep her in the neighbor category and nothing more.