Something you have to remember is a PVS-14 has about 100 times more amplification than a spark core. When it gets dark, she will be blind, or she will have to use extra IR. A Spark Core would not be suitable for navigating woods without extra IR.
As long as the extra IR is fine for your application, then a Spark Core would be workable. It has about a 30 degree FOV, which is a little small, and the distortion will affect her a little ( keep an eye on her for safety reasons there ) but otherwise it will be OK.
I was about to recommend digital, but digital isn't really suitable due to the narrow FOV. Also kids are even less sensitive to light than adults are, so you need to be careful. It may be necessary to find her another PVS-14.
Though on the cheap side, you could find something secondhand.
Normally I wouldn't recommend something expensive for a kid, but in this case, it sounds like it might be necessary. If you get the core, please let us know how it goes.
David.