As a soon-to-be mother-in-law to a daughter-in-law, I would love to be present for my grandchildren's births. However, she is the one giving birth and I am not her mother. If she is not comfortable with that or doesn't want it for whatever reason, then it is her choice. Will I be disappointed? Probably, but that's okay. She isn't obligated to do things that make her uncomfortable or unhappy to keep me from feeling disappointed. I would hope that my son would get some photos that would allow me to still see my grandchildren's first moments, even if I'm not physically in the room, and that will have to be good enough.
No woman should ever be forced to do anything she doesn't want to, regardless of the circumstances. But when it comes to something as vulnerable and sometimes scary as giving birth, she especially should feel like she is the one making the big decisions, such as who will be in the room when she gives birth.