Keep in mind that a week is a really short amount of time. It very often takes kids a few weeks to adjust at her age.
I know the teachers asked you for advice, but I would be very surprised if your daughter is the first child they've encountered that struggled with napping in a new situation. Most children her age have never napped in a room full of kids before. I'm sure they have some tricks up their sleeves but thought they'd ask you for ideas in the hopes that one of your ideas might work.
It's really hard when your little one is adjusting to a new situation like this. I remember feeling very responsible for every little thing when my youngest started daycare at 2 1/2. The director let me know that while the teachers were very experienced and that my son wasn't doing anything strange or out of the ordinary. It took a few weeks, but he adjusted to the new routine and napping there and began jumping out of the car as fast as he could to get inside.
Your little one just needs some time. If you think the pack-n-play would help, go ahead and ask them about it. But keep in mind that her teachers might rather just get her used to the mat knowing that if they use the pack-n-play now it would just be temporary and she'd have to get used to the mat eventualy.
Hang in there, but she is going to be fine :-)