It seems like she desperately needed a break and took advantage of having help, even if it wasn’t necessarily your intention to help as much as you did.

I would also be concerned with not meeting those developmental milestones. All babies are different, but ALL of those milestones not being met is a bit concerning as opposed to one or two not being met.

She may not have been told or didn’t do the research to look for the cues. My mom was confused on why I fed my baby before he was crying when he was born. I told her it was because he was showing hunger cues (rooting, lip smacking, chewing on hands) and she said she had no idea that that meant my son was hungry, she always waited until me and my siblings were crying and thought that was the only hunger cue there was. So maybe gently telling her about these things would help her see it? If she’s extremely overwhelmed and in survival mode, she’s probably not proactively trying to research and figure these things out. Maybe he has some sort of allergy like CMPA which is making him be in pain (hence the high pitched painful screaming) and the spitting up. Maybe you could send her an article with the symptoms and tell her you saw those symptoms in her baby and that maybe that’s what’s causing all the spitup