you are not leaving her with "just anybody" so no need to be nervous. These people are trained and deal with little ones EVERYDAY. Its not like you are leaving her for the entire day and not be able to know what is going on. You are free to go anytime and pick her up or just check in to see how she is doing. It is good for them to be "independent" and try new things...she will have fun meeting other kids and participating in the activities. Make it a balance...leave her for a bit, go do something fun for you, pick her up and do something fun with her and then take her back for a bit.
Enjoy your trip!