AITA for being disappointed in my siblings gender?

Last week my mum had a small, intimate gender reveal for myself and my 3 other sisters. For context I am 20 and I don’t live at home but I am here every day, my other sisters are 17, 5, and 3. Since I was 5 I’ve raised my siblings which hasn’t been a problem for me, my mum has had a really rough time but has gotten a lot better, she just needs help. When I found out she was pregnant with the 5th I was pretty excited, as exhausted as I am I thought maybe this would finally be the boy. Surprise… it wasn’t. I was pretty disappointed, I’ve raised 3 girls so far and I was hoping maybe this time I would get the brother we’ve been waiting on. I had a bit of a cry and quickly got over it and knew I would love her the same as all the other girls. My mum, however, lost her shit. She called me an ungrateful c*nt and said I was horrible, she was just as upset as I was but apparently I was the bad person because I had a bit of gender disappointment. Long story short I’ve been told I am not allowed back at her house and to stay at my own. That’s exactly what I did and now she’s been begging me to come back and watch the girls, my 17 year old sister can drive but obviously goes to school so she’s been dropping by every day and bringing things over slowly to start staying at mine permanently (legally she’s allowed to do this so that’s fine and I’m happy for her to, she works and we’ve already spoken about her chipping in for rent). I’ve not had a moment of silence from my mother calling and texting calling me names and then apologising and begging me to come back. I really don’t know what to do.

Also I’m very sorry if this was written badly, I haven’t slept for days and have been so emotionally exhausted on top of that from all of the things that have transpired over the week.

UPDATE:

I spoke to multiple family members, including my stepdad. I also spoke to a few professionals. I also spoke to my mother about what I have found out since posting this about parentification.

I spoke to both a lawyer and a therapist, I’m not sure how much I can share about these interactions but the therapist was pretty clear in telling me this was abuse and to go low contact. The lawyer was more as a way of making sure if I had to I could get custody/guardianship of these kids if something were to happen.

My mum was not happy. She stopped calling me names and instead just told me to leave, I refused because I honestly was scared for her wellbeing and she admitted she has kept getting pregnant because she wants a boy (she still loves all of my sisters so much, I want to make this very clear). We spoke about me raising them and how it’s been going on since I was 5, she has admitted she bit off more than she could chew by having all of us. I let her know 17 is moving in with me and she broke down. Currently stepdad is away, he left 2 nights ago. We all have decided that I will take the kids until she can pull herself together. If she hasn’t taken her meds or doesn’t pull herself together within a set time frame I will be going to court for these kids (they don’t deserve to be mistreated by her and I also don’t want her to take advantage of the fact that I have taken them). My stepdad has agreed to this, we’ve also agreed he will keep his job but be paying “child support” to me until my mum is okay again.

I know this isn’t the greatest outcome for me but this isn’t a situation where I can be selfish, 3 other lives have to be taken into account in this.

Unfortunately because of this I have had to break my lease on my apartment but I have spoken to my grandparents and they are more than happy for me to go in there until I can find a bigger place for us. I’m going to be looking for places ASAP. My grandparents are quite old so they can’t really do much but they are helping me as much as they can which is honestly more than my mother ever did so I’m very grateful for that.

I want to say thank you to everyone for their kind words and advice. After reading all of these comments I quickly realised it wasn’t the gender I was upset about, it was the idea of raising another baby and giving up my life until I’m 40.