What does she look like when she isn't under saddle? Does she extend at all when lunged or round penned? It could be that it is just her natural gait, you may be able to get a little more extention but if it's her natural gait then you won't get much.
If she extends more when she isn't under saddle then it could be on of two things that I can think of. One, something with the saddle is pinching and causing pain. Or Two, you are getting in the way of her movement.
From what I can see you are trying to get her to frame up with your hands but aren't helping push her through with your seat. Collection isn't about forcing the head into fram, it's about getting the whole body moving from behind and then if she is collecting through her body the head set will come from that.
Anyway, my suggestion is use your seat more, do more sitting trot/canter and push her up with your butt and legs.
Hope that helps.