My cousin is having rage fits and lashing out at her childhood, what can I do to help

My cousin whom is in her mid 20s has started acting out and throwing temper tantrums ever since around the end of last year. I hate to see her act this way as we used to hang out together a lot and she’s one of my best friends. She now seems depressed and doesn’t really wanna do anything that we used to do before. And I know she has been damaging her relationship with her mom as well. I will be honest ever since she randomly started this having this behavior she has been really unstable and just really hard to deal with. Long story short out of nowhere she has been continuously bringing up her childhood regarding how it sucked so much and that she will never get over it. And that she just happened to be the “unlucky” one that had her world turned upside down. And that her childhood will always be a “stain” in her life. I don’t want to disclose too much of the personal details but I feel like to paint a clear picture I should at least talk about some of the background. (At least the things/issues that she was telling me)

So basically to keep it simple she resents her step dad lot. And she might sound a little snobby but In her mind she used to have a really happy life, she was very spoiled and everything was good until her mom remarried when she was little. They moved out of state and life has completely changed for her. Everyone said her stepdad was a really loving and caring person (which I can honestly vouch for as well) but she disliked him wholeheartedly all because when her mom married him shortly after he was unemployed and ended up completely relied living on disability and benefits. He had just a little extra income from being the sole caregiver of his elderly parents. In her eyes her step dad was a lazy unmotivated “loser”. She says her childhood ended up being filled with so much financial hardship, embarrassment and just extremely unpleasant memories that stemmed from all of that. She also resented her mom for creating this new family. She said she will never consider or accept him as real family because it’s an embarrassment for her and that he doesn’t even come close to any of her real family at all. (Now of course I don’t know the whole story or what the causes or reasons for any of her family situation is, this is just something’s that she shared with me throughout her childhood)

Her mom ended up divorcing her step dad when she turned around 19 (I don’t think it was on bad terms though) and she has started acting out all of a sudden because I guess her mom and step dad still remained good friends after the divorce and occasionally she will borrow money from him which I guess was the trigger point for her. As you can probably tell, she thinks it’s a major shame that her mom is going to her step dad for money. Someone in her mind that stood so low and was a representation and causes for all her crappy childhood. And she is now incorporating her childhood issues into every little thing that her mom says or does. She will find a way to bring it up and blame it on her past. And this is causing a major relationship damage between the two of them. And I know they love each other a lot.

So without going into any more personal details, I just really need some advice. How can I help my cousin come out of this almost demonic state? She is now not functioning right and has been distant at times and when I ask if she wants to get out and hike or go shopping together, most of the time she is not in the mood. Now I think this is very important because she has moved to a new city couple of years ago due to her job and she says she’s been just loathing and hating the city so much, and that her job has been very stressful as well but she’s been dealing with it. I’m not sure if this might’ve been a trigger factor for her crazy behavior but I just need to know what I can do for her. She’s ruining herself and her relationship with her mom, and she knows I am there for her but I feel like this is not enough and it’s not helping. And honestly I feel like she should’ve not thought and treated her step dad that way but I didn’t want to judge her because it’s very obvious that something is bothering her. I’m not sure if this whole childhood lashing out is just a mask for something else that she’s going through right now because all that was a long time ago, or if she’s having personal issues but she doesn’t wanna see a therapist either because she says there’s nothing that can be changed about her past or her resentment for it. And that there will always be constant reminders for it. She said she was deeply scarred by the difficult and hard childhood she experienced and she just ever since developed this deep hatred for her stepdad. And she now is projecting this emotion onto her mom for “creating” all of this.

Advice is needed please! I feel like I’ve done all I can to be there for her but it’s not working and I don’t know how I can help her move on and get back on track.