If I had to weigh which factors were more important now that we have 40GB Thunderbolt 3 and being a very amateur film-maker myself:
- CPU
- then RAM
- Then GPU
- then Storage (so long as you go SSD)
CPU is still king in almost all tasks for me. GPU shines in Final Cut Pro when I'm trans-coding / analyzing video OR exporting. If your daughter is okay with overnight exports, then a GPU is less of an issue but the time she is physically clicking around will require a beefy CPU. Still, the i7 is adequate for this so long as she isn't working in HEVC / 4K. My 2015 Core i7 4Ghz machine w/ HEVC & 4K suffers sometimes but it's not awful.
RAM, you have that covered but at least 16GB and go 32GB if you know she'll be doing a lot of filters, color work, multi-cam, soundtrack and such.
GPU, it'll benefit you but less so than CPU. Unfortunately both CPU & GPU are locked in forever.
Storage, I. have a 3TB Fusion Drive on my current iMac. It's the only bottle-neck on my machine. I use about 1.5 Terabytes of it with a NAS in the basement. I have original Thunderbolt so haven't gotten into the plug-in SSD space now. I work on the internal drive then dump everything to the NAS when I'm done with the work. With a Thunderbolt 3 Mac, you could go 512GB SSD or even 256 just make sure everything system / application related fits on the drive then utilize a 2TB Thunderbolt 3 SSD as her working drive and it'll be very fast and work just fine. That can be a Christmas gift