I was curious about how an age range had been determined and why there was such a long interval in the estimation of how long the body had been there, so I became interested in how they determined the age. I found this article:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2871409/
Anyhow, this is a pretty technical article, most of which I did not understand. However, teeth can provide clues not only to the age at death but the sex and time of death of an unidentified person.
Maybe much of the stuff discussed in this article has not been done in this instance (yet) and maybe won't be done. It always puzzles me that the age range can vary so. It is understandable that the time of death is more difficult to determine. Still one wonders about the resources, both in terms of funding and time allotted on each unidentified person.
Here's how they were probably able to tell:
1. Your wisdom teeth don't erupt until you're 17 to 25 years old. Her wisdom teeth may have either not erupted yet or were still in the process (which would give you an idea of her age range).
2. The pelvis is also a good indicator of age because, when girls hit puberty, their hips start to become wider and the pelvis becomes "deeper". Girls generally finish puberty around 15 - 17 years old, so a fully developed pelvis tells you you're dealing with someone who's either that age or older.
3. The clavicle (collar bone) doesn't finish fusing until you're 21 - 25 years old. If you have a skeleton whose clavicle isn't fully developed, you know you're dealing with someone who was fairly young when they died. Combine this with the developed pelvis and the wisdom teeth, and it's a pretty safe bet that you're dealing with someone around the UID's age range.