First Sleepover: How to Help Your Kid Deal
If you don't know the parents, call them to introduce yourself and your child. Let the parent know if there are any issues that might affect your child during the sleepover such as medical problems that might require medication or certain dietary issues and food allergies. Additionally, if your child is a sleepwalker or has night terrors, make sure to let the hosting parent know so they aren't caught off guard and can keep your child safe.
Your child should pack pajamas, toothbrush, toothpaste, hair brush, small soap, a change of clothes for the next day and any sort of comfort object that your child still sleeps with (teddy, blanky, whatever). Check in with the parents to see if you need to send your child with a pillow, sleeping bag or comforter. Don't expect your child to bathe or shower during a sleepover ... or to get a good night's sleep. You remember sleepovers, right?
Also, make sure she has a way to reach you at any time during the course of the night. When you drop her off, make sure the parents have your phone number, too.