Went through a similar situation, maybe I can help. Sorry for the book.

My father was mentally abusive and cheated on my mom. It doesn't sound like your dad was abusive, but nonetheless here is what I went through, and how I dealt with it, maybe it can help you.

Keep in mind that I was in 7th grade and my brother was in 9th when this all started so my mom was trying to raise kids and work through this shit at the same time.

It may be a while before she's "normal" again. My parents were married for 17 years and divorced around 8 years ago. My mom was totally emotionally and mentally fucked for about 6 of those. She went through 7+ relationships and two more marriages before she finally gained some sense of who she is again. I know what you mean by saying you're her therapist, it feels like that. Hell some days it still does for me, but she's so much healthier now.

If they had an abusive marriage, read the next paragraph. If they didn't, it might not apply to you.

You might get frustrated, you might hate her fucking guts some days because you think "why can't you just get over it, it's been 4 years and you're still a total wreck." You might get compared to your father when she's mad at you over the fact that you ate the last of the eggs and "we can't fucking afford it" or you didn't mow the grass and now "you're a lazy piece of shit." She's emotionally unstable, she's so used to being abused, now she is abusive herself. don't try to use logic to understand her way of thinking. Learn to shrug it off. Try to be calm all the time. Try not to yell back, doing that will just make her more angry. Don't let yourself get run over though, dont lay down and allow her to abuse you, just try to be calm, and talk, try to make her see reason. I've been my mom's emotional punching bag a number of times, it hurts worse than anything but I also understood that she didn't really mean a lot of it and she's trying the best she can to get better, because she knows she's messed up. Have faith in that. She loves you.

The biggest thing you have to understand is that you and your siblings are all she has in the entire world, you're literally her guardian angels. You're her defender and her rock, you're her shoulder to cry on. You've been there through everything, not just the divorce, you were there day and night through the marriage. Because of that she feels like you're the only person on Earth that can possibly understand her, and she's going to rely on you so heavily. You have to be strong.

It's okay to not have to answers to the problem, it's human to be frustrated and tired. It's alright to be mad that she still isn't over it. Just don't get mad at her for it. I didn't want to listen to her cry about it anymore after the 3rd and 4th year she was still talking about it. But I did, I had patience because we're family. She worked her hands to the bone to provide for my brother and I. I always listened to her. She used to ask "When will I be better? When will it stop hurting?" With tears in her eyes, and all I could say was "I don't know, mom." because I honestly didnt. Sometimes I would have something great to say, most the time I didnt. I just listened to the same broken record over and over because she NEEDED me. Just like I needed her.

This last part made me feel like I was trying to give you my sob story, and I really wasn't, but I didn't know how else to write it. Sorry if it comes off like I'm making your situation about me

Keep her safe from the fucking vultures.

This is where I fucked up, because I didn't know, and because I was so young. It's a big reason why my mom was in a bad mental state for so long. There's men in this world that will prey on women that are broken down, and that will leech off of them emotionally, financially, whatever. My mom was married to her second husband a little over a year after the divorce. She was still broken, and he was a total piece of shit. They were married for two years before they split, and all he did was bleed her of 20 thousand dollars and mentally abuse her more. In the time that they were married I never really got to know him. It's not that he was an asshole to me and my brother, it's just that he didn't give a fuck, she finally decided to divorce him after he was a dick to me one night. Her third husband was very wealthy, but kind of a dick to my mom. He immediately tried to pit me and my brother against eachother by playing favorites between the two of us, he was a total dick to my brother, but super nice to me, and they divorced after 6 months. What I realized after that was that she got rid of guys that fucked with her kids, so I used that. She didn't date much for the next two years.

Her mental state improved vastly when she wasn't dating, but she was still pretty messed up.

My current step dad came along my junior year of highschool. I didn't like him at first because I didn't like anyone trying to date my mom at this point. But he was genuinely nice to my mom, and genuinely nice my brother and I. It took a little but he grew on me and now almost 4 years later I love that big fuck face. He's helped my mom grow so much, she still has emotional episodes but they happen like, 2-4 times a year, maybe.

That's pretty much it.

I don't know how much this applies to you, but I hope at least some of it helps.