Lots of judgement, self-righteous talk and virtue signalling going on here in the comments.
Grammie2, I am not surprised you are feeling upset and exluded. DIL is being, at the very least, discourteous and unfair. Maybe it's natural for her to want her mother. But courtesy is being conscious of others' feelings and needs.
OF COURSE an infant grandchild should have the opportunity to bond with her grandmother and grandfather in her early life.
And OF COURSE a first-time grandmonther would want to spend regular time with the baby. Once in 8 months is an UNCONSCIONABLY insufficient baby time to allocate to the mother of your partner (what disrespect!) and for a son to not think of his mother's presence in his baby's life.
I don't care whether boundaries have been crossed... EVERYBODY is learning in this situation, and everybody needs to be sensitive and a bit tolerant, not just poor old Grammie.
I wouldn't be making excuses for these two thoughtless young people. There's no excuse for rudeness.
Grammie2 - it isn't any wonder you feel hurt and excluded, whatever is behind this treatment of you. However, some of the virtue signallers above are right, nevertheless... carefully have a talk with your son, ensuring no blame is laid. That would stuff things up right royally. He is your liaison with the young family, though, and your first port of call (though I hope you'll be able to begin building, step by small step, a good relationship with DIL, whether you like each other or not).
There is nothing wrong with reminding your son gently that his baby would benefit from a relationship with all his or her grandparents and that you would love to spend some time with the babe, but you need him to let you know when it's the right time to come.
Extended family is terribly important for children, and I do hope your son and partner begin to see that basic politeness would be a good place to start mending the tear in the family fabric that they haven't as yet bothered to notice.