she doesn't use it to collect herself, she hasn't yet learned "true" collection
??? Nor should she have, at the level she's currently working.
If you're using "collection" in it's dressage sense, it's entirely appropriate for this horse to not be working in collection, as it's at Training level.
Teamfire, based on the video, I would say your initial impresson from the photo is accurate - she does seem to lack something behind. She also seems to lack the forwardness and fluidity I would like to see at her level of training.
She might very well make a nice Training or First Level horse, but I agree with Spyder, I think she'll struggle to do much more than that.
So if your goal is to move farther up the levels, I might keep looking.