Since the OP's DD skated at UDel, we can assume she's a US skater.
The age cutoff is in the Rulebook, which is valid through June 30th, 2019.
http://www.usfsa.org/content/2018-19%20Rulebook.pdfOn page 193, it says:
6450 Juvenile Singles and Open Juvenile Singles
Note: Open juvenile singles events are considered nonqualifying events and are held at a regional championship only at the discretion of the local organizing committee.
A. Test qualifications as of the closing date for entry to the regional championships: Juvenile moves in the field test or higher, and juvenile free skate test but no higher.
B. Age requirements as of Sept. 1 prior to the regional championships:
1. Juvenile: 12 years of age or younger for girls; 13 years of age or younger for boys
2. Open Juvenile: 13 years of age or older for girls; 14 years of age or older for boys
Age cutoff change proposals can be found on Members Only before the meeting.
After the GC meeting, the passed proposals are logged on the GC webpage here:
http://www.usfsa.org/story?id=84154&menu=leadershipIF a change in the age cutoff is proposed and passed at the Governing Council (GC) meeting in Spring 2019, it will be published over the summer in the official Rulebook.