Some of these responses are ridiculous, clearly some posters don’t live in the real world.
I have a 2 year old and I’m currently pregnant. I would never dream of making any of my parents/siblings/in-laws that are immediate family to either I or DH wait that long.
Yes, the well-being of the new mom and baby should be top priority. For that reason I won’t be having anyone other than DH and my DD at the hospital (other than if I need my sister to cover DH during labour), and I won’t be having visitors for the first 24ish hours to get a bit more settled as I regretted letting people round straight away last time. HOWEVER, me and the baby aren’t the only priority, DH (and obviously DD) is as well. He will want to show the new baby to his family, as any person with normal family relationships would. And his feelings are also important, he’s a new parent as well. So I would never dream of shutting his family out, they get the same treatment as mine.
I was in the same position as the OPs DIL with my DD. Breastfeeding didn’t go to plan and I was expressing at all hours. I still found an hour for people to visit every week or so.
OP, I would do as the sane pp’s have said. Give it a couple of days and ask if you can come round, make it clear it’ll be no more than an hour tops and take a little gift for your son and DIL as well. Hopefully once you’re there and DIL can see you aren’t going to be grabby with the baby then she will calm down.