Female friendships?

r/

I’m 40 and my best friend of many years is 38, so we’re well into adulthood. Back when we were around 15, her first large crush ended up liking me – I didn’t like him and nothing happened but it was devastating for her and I. It’s like that was a trigger moment, since then every once in a while – not often – maybe every couple years someone would pull me aside to let me know she says cruel things about me behind my back.
She’s also gone after boys/men I was interested in, again all seemingly from that one incident in high school.
I stepped back from the friendship and we naturally lost touch for about 6 years or so, recently we’ve been in touch again and it’s been great. She seems to have matured so much and gives fantastic advice and has been an incredibly thoughtful friend. I’ve loved having her back in my life.
Lastnight we were out, and I overheard her in a bathroom again talking mean about me. It’s honestly frustrating and a little heartbreaking.
Should we just not be friends? It’s not something that happens every time, and this time she broke down and blames it on her insecurities. What should I do, if anything ?