mother in law doesn't care about naps

Sbrow
So today my inlaws watched my 9 month old son. My husband and I rarely get alone time and they said they would watch him so we could go out. I brought him over around 1030am and told her if I wasn't back in time that he needed to go down for a nap around 130pm. Well I didn't get back till around 3pm cause we got stuck in really bad traffic. I asked her if he had napped and she said no; I asked her if she even tried putting him down and she said no. So by that time he had been up for 5 hours. She acted like it was no big deal but I had to listen to my son cry the whole way home because he was exhausted, and when he doesn't nap good during the day he sleeps like crap at night. I'm a little hormonal right now ( aunt flow time) so I don't know if my anger is justified. I want to tell her that because she doesn't care about naps (which I consider vital to his well being) that I don't want her watching him for a while. Am I crazy? Sorry for the long post.