Friend talks a lot about how her old friends mistreated her. Is this a red flag?

I've noticed my friend of 5 years talks a lot about her old friendships. When she and I meet up, she'll just end up talking nonstop about her past. Usually stuff about her old friends and childhood. A lot of it is telling me how old friends mistreated her. She also does this thing that I find annoying where she just says the old friend's name without any context. Like "yeah Kimberly would do that"

I don't know who Kimberly is? I don't know anyone from her childhood because we met as adults.

At first I didn't mind because I enjoy getting to know people by learning about their past. But now I'm realizing even after all these years, she still constantly talks about how her old friends mistreated her. It's also about how they were wrong, but never her. She refers to all of it as her trauma.

She knows nothing about me or my past. Mainly because I don't share irrelevant stories, but also because she's never asked.

Is what she doing normal and I'm overthinking? Or is it a little off?

I also have a lot of old friendships that didn't work out. But I do not bring them up to my current friends because they don't know them? I also just don't speak badly about them because it's been so long.

Like we are in our late 20s and these old friendships are from middle school, high school, or college.