I think something that you may need to take into account is her situation and her mental state. Being a young parent can be wonderful and it can royally suck ass at times. It can be really stressful. With my daughter I was in my mid 20s and lived close by my parents. Before they went insane they were very helpful with me and watching my daughter while I worked and a couple of nights a month they would let her sleep over. What would I do while she was gone? Stay home, sleep. Mentally unwind.
Hell, I'm 42 now and with my 3 year old literally nobody steps up to offer to help us. I'm pretty much a professional parent at this point and I still have times where I get stressed out and would love a break for a night but I know it isn't going to happen. My wife and I have 3 sets of retired parents who all give zero fucks about anyone else now and are off vacationing constantly. Great for them...
...but every parent has their limit and needs breaks. Some need them once a week and some need a break once a year.
When they reach out for help they are stressed, especially if all they do when kiddo isn't around is stay home and rest.
As a future potential grandparent I would totally rather have the little one over for a night to give mom and dad a break instead of getting a call some random morning that somebody snapped and drove over a cliff with baby in the back seat.
If you have major issues helping out watching the grandkid then cool but maybe help point the daughter in the direction of other folks who can help, too, and realize that she is probably in over her head and needs time for herself, too.