To answer your questions in order:
1) There are free video editors out there that are easy to use and which are comparable to iMovie or Windows Movie Maker. There are also free video editors out there that are very useful but not as easy to learn such as...Blender, surprisingly.
2) Some use CPU, some use GPU to accelerate specific functions (either natively or through plug-ins), but GPU usage is not a standard thing across all NLE (Non-Linear Editors). On top of that, different GPUs have varying levels of what they can accelerate AND different levels of quality of doing so, so just having "GPU-accelerated" on the box should not be enough to automatically lock in that choice.
3) Yes an i7 is most definitely worth it over the equivalent i5 model...IF it's one of the i7's that support hyperthreading (not all do). In many cases, the biggest difference between the equivalent i7/i5 model is that the i7 can run twice as many threads as the i5. E.g., a quad-core i5 can run 4 concurrent threads, while (most) quad-core i7's can run 8 concurrent threads (4 full speed, 4 reduced speed), which often translates to a total of about a 30% increase in performance, but that also means springing for an i7 is probably not worth it unless you can get it for only 30% more money (or less).
Reluctant as
@GasBandit might be to admit it, he's probably not wrong. You can get a 13in MacBook Pro with Touch Bar for $1800* minus whatever her student discount can cut off the price, but as far as getting Final Cut for $300...well, because she's a student Apple will throw in full versions of Final Cut Pro X, Logic Pro X, Motion, Compressor, and MainStage...
all 5 together for just an additional $200. That's almost like paying full price for the apps and getting the computer for only $1300. Apple is being SUPER aggressive in the "I'm entering college" market right now, but yes, she may have to buy a couple adapters because of the new USB ports not working with older hard drives, etc. If she wasn't going to be doing video editing, then there would be a lot more more (cheaper) models of Windows laptops to choose from, but that app bundle almost makes it a no-brainer, especially since Pages, Numbers, and Keynote** are also included for free with every new Mac now.
--Patrick
*The base model should be fine, if she wants to spend any extra her first priority should probably be the $200 extra to go from 8GB to 16GB RAM. There is an i7 option, but this is one of those that's really just a faster i5 with an i7 label slapped on it, not worth a 17% price increase for only a 10% speed increase, IMHO. And if she is going to be doing a lot of video/audio editing, she will definitely want the touch bar. Having one-finger access to being able to scrub the playhead is worth it right there.
**Apple's versions of Word, Excel, and Powerpoint.