Is it possible that when you're getting up to feed and diaper the new baby at night that your pup wakes up and you don't hear her? Perhaps if she's awake in the other room, and not sleeping through her urge to pee, she is going in the crate because she is not being taken outside. Maybe before the baby came, she could hold her pee because she slept through the night? Also, please be patient like others said and remember she's just a baby herself and can sense your frustration and anger. I'm sure you're exhausted, but this too shall pass. BTW, congratulations on your newest little addition!! Good luck
Oh, and please give her food and water at regular intervals, she is too tiny to go all day on one meal.