I don't see any reason why she couldn't be a decent jumper. Irish Draft/Warmblood crosses often make good jumpers, as well as event and hunt horses. She looks proportionate and I don't see any glaringly obvious conformational faults. It looks like she has a reasonable bascule over the jump in that one picture, though I'm not sure what the rider's doing. It looks like the rider smacked her and forced her over that fence, and it looks like her take off point was really close to the fence. I feel like this is a rider issue first, and that the horse may need some gymnastic work to help with her rythm and approaches. If that's the case, it's nothing that can't be fixed. At 17.2 hands working up to 3'9" courses should not be too much of a challenge for her, as long as she has the heart for it.
It is true that drafts and draft crosses can be heavy on the forehand, which can make it tough for them to jump, but this is not true of all of them. This mare does not look too heavy in her build, and even horses that want to naturally move on their forehand can be encouraged to get off the forehand with proper training and exercise. It can be a challenge but it is not an impossible task.
My own horse is a Shire/TB cross and she is heavier than the mare you're considering. My horse loves her forehand, and the problem was perpetuated by an old hip injury (since fully healed but her way of going was habit), and even I have been able to get her off the forehand enough to clear some fences. I have jumped her up to 3'6" already and only took a few months worth of weekly jumping lessons with her. She's 17 hands tall and hops over anything lower than 4' like it's nothing. Keep in mind, not all draft crosses are like that, but they can be found.
I suggest you give this mare some more thought. If you're hesitant to travel a long distance to see her in person, request more videos first (specifically a jumping video).