Cute mare; looks like she has it in her to do bigger fences when you are ready. I like that she's even in the knees, even over a smaller fence. She uses her neck well. She looks like a likeable gal.
Are you wanting to do hunters, jumpers, CT, or all of the above? The hunter ring is going to be the least forgiving about mistakes in form. I agree that your leg has slipped back, which has thrown off the rest of your body, right down to your line of sight. Once you get your legs sorted out, the rest will quickly fall into place. Might shorten the stirrups a hole. Your back does appear a bit rounded, but are you wearing a crash vest? That might be changing the appearance (but good for you if you are wearing a vest). You have a nice release and you don't look tentative at all! You look like you are itching to be put on bigger fences, am I right? :bgrin
Back when I was jumping, I found it so beneficial to really work on my strength. Sit-ups were a must for me, as they strengthen your back as well as your belly. Squats are good too (when you are young and have good knees). Being lunged without irons and reins is good for balance and settling the legs. Trotting cavaletti poles in 2 point until your legs burn, and then trotting some more will also help. If you don't feel sore muscles the morning after a jumping lesson, you aren't working hard enough (at least according to my sadistic trainers)! Any chance you get (stairs, curbs, etc), sttttretchhh those tendons in your calves, the ones that let you drop your heels.
It looks like you and your mare are having fun, and that's great to see; thanks for sharing. OK, I'm gonna have to break out my old photo albums and remember those wonderful days.
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