Help! Baby won't sleep at my parents house

Help me cranky napless baby! V started going to my parents house during the day last week. We brought over the pack and play for her to nap in for her am and noon time nap. She has never napped there and I figured she may cry a bit but she would eventually fall asleep. Nope. It's been a week and she just cries, she won't nap in the pack and play. By the time I pick her up in the afternoon she is a cranky mess. Help I hate to see her struggle so much. I don't know what to do, I was thinking of getting her a mattress for the bottom to make it more comfortable? I'm also concerned that my parents will scoop her up if she cries for more than a few minutes , which won't help her either. Please any advice, I just want my girl to sleep again. Oh and my parents have taken care of her since I went back at four months and besides nap time she is very happy going there.