When I went to live with my girlfriend a few years ago I was initially surprised by how she got very angry (using a very aggressive tone, shouting, ecc..) when I did "something wrong". By angry, I mean that she might use a very aggressive tone and shout with rant lasting several minutes. She never got physically aggressive or anything of that sort.
Just to give you some examples of the things that could make her angry were me saying some inappropriate jokes, the fact that I was frequently late or the fact that I was frequently a bit absent-minded or absorbed in other things.
While recognizing my mistakes, I made her notice that her reactions were somehow excessive and we reached the conclusion that I should be more careful around here in some contexts and at the same time that she should take better care of her behavior when annoyed or angry.
After a few years, now the situation is kind of different. I think I really improved with her and I am much now more careful, she also completely recognizes this. Unfortunately, at the same time, she worsened her behavior. She still gets angry, but now over smaller and smaller issues. Also, while at first, it happened mainly when we were alone, now she's doing this when other people are around, even friends or relatives, making it even more painful and embarrassing.
I never got so irrationally angry at her and never shouted at her in any way. When she gets angry and starts shouting I generally just shut up until she's over and then tell her that she went mental again. She generally answers at first by trying to justify herself in some way and then by recognizing that I'm right and the issue at hand was ridiculous (or sometimes even non-existent!) and by saying she's sorry and will be more careful in the future. Unfortunately, after a just a few days, we are again dealing with the same situation.
I think it's important to add that she doesn't behave in this way with her friends or acquaintances, while she does instead something similar with her parents. I think it's also valuable to say that she told me that her parents used to fight in this way quite frequently, especially when she was a child.
I tried to talk to her about the reasons behind her behavior, to try to understand if she just got really angry over nothing or she just has excessive reactions when she is just slightly annoyed and she seems to be more inclined to believe the latter. As a solution, I really tried to talk to her about this a lot and even suggested that she could visit a specialist (something she is now considering).
Is there any other thing I could do to make her improve her behavior?
EDIT, a few details I added in the comments:
An example of how she may get angry over a small thing:
She may be looking at something funny on the web and asks me to join her. While doing it together it may come to my mind something related that I'm sure she may appreciates and I suggest her to search for that. Maybe she doesn't do that immediately (and that's fine of course) so after a few minutes I suggest it again and she flies off the handle. She may start to scream about how she wants to look at what she prefers, how she wants to be left alone, that she has already wasted too much time doing nothing, that she already had a very tough day and I'm only making it worse, and similar things.
About her childhood:
She had a very good childhood, in a upper-middle class family where she was treated like a princess. Her parents are a very strong couple, very close together. They just happened to share a lot of time together (both worked from home) and when some conflict arose they reacted by raising their voices, but AFAIK never insulting each others or worse.