YADNBU OP!
For me this is a very contentious issue and I would like to explain why...
I had similar problem with my D who expected me to look after her DCs when she wanted to go back to work part time. She did not at any time expect her husband to do any child care. pick ups or drop offs even though he has a very flexible job!
This was after I had worked over 35years full time and had to stop work due to serious health problems.
She did not for one minute consider the effect it had on my health in all and tbh she didn't really care.
At no time was she appreciative of any of the help she received from me and told me that's what I was there for!!
I do not know where she got the ideas from because I paid for all child care for my DCs when I became a single parent in my early 20's(DCs aged 3 and 1) and did not rely on family or friends as they were all working full time jobs as well.
To do this I had to work initially in a low paid job, walk everywhere, no car, holidays, no expensive nights out.
I have had many conversations with parents of adult children who are worn down by the demands put on them by the ACs wanting full time childcare from their parents and see it as a right rather than a privilege.
Many parents are too scared to say anything because their ACs will get angry and not let the parents see the grandchildren.
This happened to me nearly 3years ago by that time I was bedridden and housebound.
I have seen my Grandchildren no more than 3 times a year since then and my daughter even less.
If I had known what would have happened with her cutting contact I would have refused in the very beginning to have them at all and taken more care of myself and my own health more. Instead of bonding really close with the grandchildren then not seeing them hardly at all.
So my view is put your foot down OP and don't allow your DD to make too much demands on your time for child care because it will build resentment on both sides. Your DD will expect it and you will soon find it too difficult to cope with a youngster.