"Everyone is voting OP NTA and the mom TA on the assumption that the mom was storming in furious at her when she was probably just looking a bit visibly frustrated by her own circumstances (having to deal with a cranky baby and all)."

OP literally said that she looked furious. You can certainly accuse OP of lying or misrepresenting what happened, but as her account is the only one we have and the only reason that we're discussing any of this, yes, I'm choosing to take her at her word.

"People on this sub sometimes genuinely have no reading comprehension or ability to interpret situations."

You're faulting other's reading comprehension for accepting OP's version rather than loosely interpreting the story through the lens that you've chosen? That's not what reading comprehension is.