You are very tense in your upper body, especially in your shoulders personally I think that this is destroying most of your position.
A) look up because when you look down you slouch
B) open your shoulder (this will also come with looking up)
C) relax breath and let all the weight sink into your saddled) hold your stomach muscles and let your breast come forward and our and your shoulders back relaxed and elbows softly bent.
D) take your leg back formt he hip.
E. Put weight into your heel.
* it looks to me as though you ar wearing full gum boots? The rubber boots? I could be corrected but on the point those boots are terrible for position, the are loose and not fitter and the restrict your heel and foot movement refraining you from getting your heels down and therefore bringing your knee up and loosing your leg position completely.
To me your horse looks very tense as if she has been pulled into the frame and not just sitting there relaxed through her back and on her quarters. It looks like it is coming form the head only. Being on the bit is not just having a round head fram but working through the hind quarters and being pushed into the bit rather than pulled. HTis gets them through the back.
Hope I could help you both have awesoem potebtial good luck