Hi Amy!
Well, since it will be really early, her options will be limited, but still very exciting!
What most people do is hop on the monorails after the race begins and head to the Magic Kingdom. There, she can watch runners and see you as you run up Main Street U.S.A. toward Cinderella Castle! It's truly the highlight of the race:)
The shops along Main Street will be open, so she can browse around there for a bit, and then head back (using the monorails) to see you finish in the Epcot parking lot.
Alternatively, if she wanted to hang around the start/finish area the whole time, she could purchase the Platinum ChEAR squad package to have use of the Race Retreat tent once runners begin. You can find this information on the
Princess Half Marathon website by clicking on the tab "SPECTATORS", and then "ChEAR Squad".
I hope this helps! Please let me know if you have any other questions.