Short list the people who are and have stood up for you, and who believe you.
Those are most likely those you love best, and who are most important to you. CALL them, and thank them. No other purpose than just to thank them for being your rocks, and guidance, and sanity. Let them know how much you appreciate their love and their friendship.
Enjoy your life. She can try and cause you as much pain as she wants, but if you're happy... she fails. She's trying to hurt you through others, DO stick up for yourself, but there is no reason -as you said- to loop everyone into a big drama circle. Just, as things come up, set people straight. No need to put on a happy face if you're *actually* happy.
I've had something similar in my own extended family (I ignore many of them... I have enough fools to suffer). I just sort of pretended they didn't exist and went about my life with the members of my family I DO care deeply for and who care for me. The above, is *exactly* what I did for 3 years. Finally, one thanksgiving, my dad lost it on the backbiters. He threw his napkin down, stood up, read them all the riot act that he was NOT going to sit here and listen to people attack his daughter, and marched out with my mother. My sibs and cousins clapped and got up and left also, and the other side of the fam erupted into yelling and screaming while the "fence sitters" gaped. It became super apparent that thanksgiving (which was the 3rd I didn't attend, because the loonies would be there) who the loonies really were. I head this story from no fewer than 15 people. My mom and sibs and cousins.
<grinning> From that thanksgiving onward there has been peace. Not that it affects me at all. Because from the time my aunt started being looney, I crossed her off my "worry about" list. But for my parents and sibs it's been a huge relief not to hear me trashed every which way at every family gathering.
I should add... I DO go to family gatherings. But I only go to ones that are hosted by the people who have proven to not be batpoop crazy. Thanksgiving used to always be hosted by my Aunt, so I never went after she began her descent into "Let's attack R.!" phase. By only going to those hosted by my loved ones... if anything drama-like occured I'd give the host big hugs, thank them for the lovely etc., so forth, and so on... express my wishes to get in touch later that day or tomorrow about getting together... and either head home or back to the hotel.
I've been told I'm "chicken", "running away", etc. My response is that "I would never be so rude as to ruin the hosts party by fighting or being snarky in their living room while I am a guest in their home."