But there again, 19 or 20 is a big jump from 14 or 15. Even if she started when she was 17 or 18, she would have grown up a lot in those couple of years.
Like I said, at this point (again, in theory) she wouldn't be in the field herself, but using her access to co-ordinate and feed information through channels and cover her tracks. She could very well be doing the whole thing from a holonet terminal on Coruscant, or Alderaan. I mean why not? That's pretty much what Palpatine did for the most part.
Even now, it's extremely hard to think about 19 or 20 year olds dying in combat, but they do. But to think about 15 year old dying in combat is a horrific thought and the business of monstrous terror groups.
How many 14 year olds do you think the French Resistance used to run reconnaissance, carry information or even fight during WWII? Hell, allot of the soldiers that invaded Normandy and the bomber crews that levelled Berlin were in the 16-19 year old range. Officially or otherwise; I know for example my grandfather lied about his age to get into the army prior to WWII. One imagines that sort of thing only increased after the war broke out.
Not sure exactly when the practice stopped, but the Royal Navy employed cabin boys of the 14-16 age range and it wasn't as if they got to go somewhere safe when the shooting started, or spared when a ship was boarded. Midshipman also started at around that age I believe, many of whom were of nobility. Sadly, history is replete with such examples and it's not just the work of third world warlords and militant extremists.