It sounds like she is getting nervous, but maybe also excited knowing school will be starting shortly and it is keeping her from sound sleep. I would do the following things:
Get plenty of exercise, outside if possible. This will help her wear off any excess energy and help her sleep more soundly.
Figure out how much sleep she requires to wake up on her own. My son (almost 6-just started kindergarten a few weeks ago) only needs about 10 hours and he functions beautifully. His sister (4.5) needs at least 12 hours, so adjust her bedtime accordingly. Sometimes overtired children have a hard time sleeping. You think they would just crash, but they don't necessarily. Weird phenomenon I think.
Make sure she is eating a well-balanced diet of fruits, veggies, proteins and grains. I notice a huge difference in my kids energy and attitudes when they eat healthy and drink water. They have more energy to play harder, thus making them sleep better. Eating healthy, exercising and getting enough sleep all work together in tandem, so be sure to set her up with habits that reinforce that. Treats are fun occasionally, but limit them. That sugar and processed junk wreaks havoc silently. I follow two blogs on the internet and facebook called Foodbabe and 100 days of real food. They are excellent and give a lot of great ideas and recipes for nutritious meals.
Check out some books from the library that are all about Kindergarten. This may help her explore her own rollercoaster of emotions about going soon. The Llama Llama books are great, Bernstain Bears and Mrs. Bindergarten Gets Ready for Kindergarten are a few of my kids' faves. The Kissing Hand is a great one for kids that may be nervous about being away from their family. You can copy from the book or make up your own secret ritual to help your daughter feel connected to you throughout the day.
At any rate, as others have said, this is probably a phase and I wouldn't worry too much about it. You may want to call your doctor just to ease your mind, but it is probably stress-related for her with all the new things to come soon. It's best that you remain positive and worry-free around her and that will help her to stay calm as well. Good luck!
A.