tbh my lad has an i5 with geforce 720m with 6gb ram and it's handled everything he's attempted so far, I'm prob gonna end up getting her more than she'll end up needing but as part of her media course they have a tv channel & are already 4k'd up with all of the cameras... which they can bring home so dont want to end up where she cant do stuff and I've lashed 5-600 quid at it
In fact they have a steady cam thing so I'll be tempted to stick it on and attempt an end of match invasion, I've told her actually to pester next doors brother as he did the same course at the same college and is now a digital media dude at the club, which could be great for her project work.
He often does the twitter btw, and I can tell when its him late night after a bevvy.
So getting just a tad technical, to reiterate, you want an i7. The main advantage an i7 has over the i5 is Hyper-Threading. Hyper-threading is basically like a virtual cpu core. So you get 4 physical cores on the cpu itself, then 4 virtual ones. This allows for 8 threads, which means 8 tasks simultaneously....and when you are video processing, all 8 of those threads will be utilized.
For gaming, lots of games still don't support multiple threads, or only support a few (not true of every game mind you), so an i5 will suffice for them (heck, even a decent dual core i3 can manage games).
For an example, have a look at my cpu (i5-6600k) versus its i7 brother. It has hyperthreading, and by default has the clock speed bumped up a little.
When you look at the gaming benchmarks, the results are so close there is barely any difference, in which case there is no reason to stump the extra cash for the i7, when at best it gives you an extra 5 fps for all that extra money. However, when you start factoring in all the multi-threaded programs, that tiny difference widens quite significantly.
http://www.anandtech.com/bench/product/1543?vs=1544
If you add even more cores and threads, then the performance only increases.
Honestly, the computer business is much like the car modifying business. The old anecdote of "I was in a car speed shop, and above the workshop was a sign - 'Speed costs money. How fast do you want to go?' " applies here.
Tl;dr Get her the quad core i7 laptop with bags of ram for the video processing tasks ahead of her. (although get her to do it on your lads i5 first so she can properly appreciate the extra speed).