Honestly, you have nice form - especially for someone self-taught!!
If your mare is also new to jumping I would keep everything low low low - cross rails (making an x out of two poles) makes for an inviting jump and teaches her to keep her front legs tucked evenly over the jump. The jump with 3 tires is definitely high enough - as it isn't about the height that makes horse or rider better, but practice and consistency!
A few things you could work on? Keep the jumps nice and low, and just trot in for your approach. It's okay to let her canter away - horses often do no matter how big/small the jump is. What you want to focus on is a very straight approach and exit. Pick a line and keep your eyes up and focused on staying straight. The bottom picture there where you're trotting in. If she's fighting with you, you could circle her at that point and keep circling in both directions until she's quiet again and then approach the jump - you want to avoid 'fighting' over speed both before and after. Also that bottom picture is a good distance where you take your eyes away from the jump and look up to keep your eyes on your exit away. In the other two pictures you're looking down a wee bit and when your eyes go down, so will hers - so always look up. Spot your jump 3, 4, 5 strides out and then look up toward your exit. You have a nice release in that you are not catching your mare in the mouth at all over the jump in either picture! Practice bringing your elbows forward as you jump - that will allow your hand to move forward either up her crest or alongside her neck, and once your elbow is moving forward when you jump you can shorten your reins a bit so you keep an even, steady contact before, over and after the jump. Last thing I can think of is that when you have the lead poles to either side of the fence, you want to always only jump through them, you don't want to jump backwards as in the top picture.
Hope that gives you some helpful advice! :) Lookin good!