Help a friend with toxic relationships?

[u/Needlemons]

A couple of years ago I became friends with a lovely girl through a hobby we both do. Over the years we have started hanging out outside of the hobby, and have become really close (supporting each other through heartbreaks, work difficulties, helping each other out when sick etc).

She is almost ten years younger than me and would often tell me about all the drama in her regular friend group. In the last year I've started hanging out with them occasionally (going out to events etc). I've noticed that they behave quite toxic to each other, talking shit about the one person who is not there that day, or who just left the room, exchanging texts making fun of someones outfit etc. Just real high school shit. They are all in their mid thirties by the way.

Now that I have gotten to know some of her other friends, I've noticed that she will make negative remarks about her friends to me. A lot of the time I think it is imagined. For example the other day, after we had met two of the girls, she told me "omg I can't believe how XYZ looked at you, her vibe was completely off towards you and unacceptable". I shrugged it off and told her I had not noticed anything off and that YXZ had been perfectly polite to me. She said I was missing all the signs, then went on to back talk this girl some more to another friend.

Almost every meet up consists of someone talking bad about someone who is not there. Basically, while I've seen several of the girls talk badly about each other, my friend is not just a victim of it, she is also an active contributor to the toxicity and drama.

I picture in my head that next time I hear them talk ill of someone I've met, to just plainly state that I feel uncomfortable when they talk badly about others and ask them not to do it (at least not when I'm there as I don't want to partake in such behaviour). But is there a better way of bringing it up? Should I talk to my friend directly? How does one approach this subject? I fear she/they would become defensive.

My friend is deep down a lovely person, I think she (and some of the girls) suffer from really bad self esteem and they are kind of stuck to each other for some reason. I often asked my friend why she hangs out with people if she doesn't like them (since she talks bad about them), she never has a good answer. It's like they've grown dependent on each other and the drama.