[23F] How do I handle a long-term friend [23F] who flakes constantly, avoids confirming plans, and gets overwhelmed when I bring it up?

Both of us are 23F and we have been friends since first or second grade. We have been more friends than not throughout the years and the inconsistency has always been part of her personality. It never bothered me this much when we were younger, but now that we are older and trying to be more mature and responsible it has become a lot more frustrating and confusing for me.

She cancels plans at the last minute, avoids confirming anything, and sometimes ignores messages for hours even when she is clearly active doing other things on her phone. I work and I am in college full time and I still communicate, so her lack of communication makes me feel brushed off.

There are several examples. We will plan movies for weeks and then she will suddenly see the movie with someone else without telling me until afterward. Once she insisted she bought the tickets and acted like she was handling it, but when we arrived she admitted she never bought them and they were sold out. When I try to address anything she becomes extremely emotional and overwhelmed. She cries, panics, and says she did not know it bothered me or that she wishes I had spoken up sooner, even though I am trying to communicate. She frequently forgets plans because she already agreed to something else, including plans with her boyfriend. She also often shows up without her card, which means I pay and then remind her to pay me back. Sometimes she does and sometimes she says she is broke until payday.

Today both of our plans fell apart again. Earlier she canceled the movie because she forgot she promised her boyfriend something. Later she canceled our nail appointment because she had to work late after calling off the day before. I ended up going alone.

Every time I bring up the pattern she says she will change. She does better for a short time but always goes back to the same habits. Since we have been friends for so long I do not want to end the friendship, but I also do not know if this dynamic is healthy anymore now that we are adults with real responsibilities.

My question is how do I set boundaries or communicate expectations with her in a calm and healthy way that does not lead to her breaking down emotionally. I also want advice on whether maintaining this friendship is realistic long term now that we are at an age where consistency and responsibility matter more.

TLDR: I am 23F and have been friends with someone who is also 23F since early elementary school. She has always been inconsistent, but now that we are older it is much harder to deal with. She flakes, avoids confirming plans, forgets commitments, and becomes very emotional whenever I try to talk about it. I am looking for advice on how to communicate boundaries and whether this friendship can realistically work as adults.