What your mother did to you was horrible.
You need to research a way to find out who you could talk to about this.
These people are friendly acquaintances you've made via your daughter's school. They are not long term, close best friends who you've known for years and years but you are treating them as if they are .
I just expect them to understand where I'm coming from and why I say what I say and why I act like I do.....but they don't
Then STOP discussing it with them.
You are dealing with unmanageable feelings and this is not helping you. Find the right people to talk to
Also recognise that these things are in the past. Hurtful but in the past and you need to stop letting them affect your life now.
All of her friends got together (planned by the parents) recently but excluded her in what seemed like an intentional way, so I pulled them up on it and now none of them want to know me
You are barging in here like a bull in a china shop.
As previous poster said. Your Daughter is your number one priority.
Stop and THINK before you do things like this. How has it helped your daughter?.. All its done is make them all take a huge step back because they are worried that your behaviour is unpredictable and it could be the very reason why your daughter is being excluded.
They are school mums and not the people to be exposing your innermost feelings to at least not in a group. This is not the way to encourage your daughter's friendships.
Think how you felt when your mum showed you up in a school talk.
People don't suddenly behave the way you want them to if you give them a big telling off. You cannot force them to include your DD by "pulling them up on it" it really sounds like you over did it .
Could you find a class or a book which might help you deal with these situations in a calm, assertive way that doesn't upset people?
If you think your DD is being excluded in class, then you need to talk (calmly) with the school.
The best thing you can do now is apologise if you were offensive to them. (even if you feel they don't deserve it, the aim is to get back on civil terms with them, and hopefully it will make life easier for your daughter.) You might even find that this helps re build the bridges and with the Christmas break it will all die down and things can go on as normal. Take a huge step back and practice being very very boring and normal around them and don't moan about your childhood in conversations with them.
Find some mums at school who are a bit kinder and see if you can organise some playdates for your daughter with their children BUT DO NOT see them as people you have to tell everything to. Try to see this as an exercise in encouraging your daughters friendships without getting so involved yourself. If you are worried about your daughter's friendship group, look at afterschool activities to keep her busy, sports or drama. She will make friends that way and it takes some of the focus off school friendships.
I'm sorry that you feel this way, and perhaps you need to take a big step back from your Mum while you sort out your feelings. Stop running after your brother and trying to get him interested and then being upset that he isn't. You are just repeating the pattern with the same results. That's his problem, leave him to it and focus on doing nice stuff with your daughter yourself. It might be that you need to focus on your own adult friendships and interests too,
I am sure there are people on this thread who have some recommendations of where you can get some help/advice in dealing with your feelings.
But please think about what you are trying to achieve and the best way to achieve it before you charge in with school mums.
If its any consolation, many people find primary school years very difficult. But you have the Christmas break to have some fun with your daughter. Don't dwell on it with her, she's a child and shouldn't have to worry about these things. Focus on your relationship with her and how it will be better than the one you had with your mum. I hope you find some relief or support soon. Best of luck