I write this as someone who has felt something pretty similar: you can't change the way she is and behaves but you can change how you react to it or what you look for from her. If talking to her might help, do that, but if not nod, smile and try to let it bounce off you. Don't let it poison your relationship with your brother either. You feel crap at the moment and having a young child is seriously hard work, especially without support but you're really not helping yourself at the moment. And you can make a choice about it.
My mum was open with me growing up that my brother (who was her pfb) was her favourite. I, apparently, ruined her figure and motherhood ruined her life. I was a difficult baby who became a difficult child, apparently. My brother could do no wrong. He was the one who was academically clever and worthwhile where I had to 'work hard', according to her. I was also the reason her marriage to my father broke down, apparently, because parenting me was so hard. (They split when I was 14 but would have done everyone a favour had it been many years earlier).
As a teen my brother stole money from my dad. My mum covered for him/took the blame. 2 days later, I was 10 mins late home for a curfew - my mum 'told my dad' on me. etc. I felt crap about myself a lot of the time.
Then I reached a point where I figured all of this was HER problem, not mine and that she was a rubbish parent because of this favouring thing. I looked around at my mates' mums and figured I'd just got a raw deal here and I didn't have to let it define me. I also had a bit of compassion for how crap her life must be but realised it was her choice. I also recognised that in some ways it put a pressure on my brother I didn't have to contend with. I also decided 'fuck you, I'll show you what I'm capable of.' I've struggled to maintain that sometimes, but it's helped a lot.
When I called to tell her I had a first in my uni degree she said 'of course you do, you probably had to work really hard and did that to spite your brother and his 2:1".
When my brother died (in his twenties) my mum (while drunk) told me that if she could have chosen which child died, it wouldn't have been him. A couple of years later when I told her I was expecting her first grandchild she told me I was ruining and wasting my education and didn't I learn anything from her about how being a mother ruins your life.
When my father was later prosecuted for historical sexual abuse and I had a conversation with my mum about it, I realised that my mum probably knew my brother was being abused and failed to protect him. Her favouring him was poor compensation for that.
I stopped looking for any approval or pride. I've also had 2 lots of sustained counselling, which helped although it felt like it only really helped with the second lot. If you can access it, I'd recommend it. It helped me recognise that I was a people-pleaser often desperate to gain others' approval and worth while expecting little in return. It also taught me I was a control freak and struggle to rely/lean on other people. Those things are probably still there, but being aware of them and working at them hopefully knocks the edges off!
But really, this is up to you - you can chose to feel miserable about it or have pride in yourself. I'm not saying it will be easy but it is a choice and something you'll need to work at. I'm now low contact with my mother and I live 100 miles away from her.
I sincerely hope that my children know they are a precious blessing in my life and that being their mum is the toughest but most important and most rewarding job I'll ever have. It's also a privilege. I burst with pride in their achievements and I hope I'll always show them that too. I hope I show my love for them every day, I certainly try to.
You're in charge of your life story and it's up to you what you do with it. Good luck.