ArtV the OP did not say she was 'shouting' I just think she was annoyed that her mother made no effort to quieten her tone in case babay was falling asleep - which is quite different.
However, with the new info, I can see OP's point better now. OP I had less than perfect parents. Dad was a selfish self-absorbed twat who was pretty much absent for a year or more at a time, from when I was 5 onwards, and DM was very loving, but young, and well....flawed. She was an excellent mother in many ways, but she definitely had lapses of judgement. Growing up I sometimes felt like I was the mother and she was the child, and it has shaped who I am today.
I think when you have just had a baby of your own all your maternal and protective instincts are heightened, and you start to remember things that were less than perfect in your own upbringing and think 'WTF did they do that? How could they? I would never do that to my child.'
When you are a child you just accept what you are handed on a plate from your parents as normal, because you have no other frame of reference, and you want to assume your parents are perfect, lovely people, always getting everything right. It's not until you become an adult, and a parent yourself that you can see that they sometimes have massive personality flaws, and made huge mistakes, and you do through a period of realisation and resentment.