Ponies are stubborn bitches. That is why we bought a mini. =]
I hate this common thought.
A. Your photos tell me that your "mini" is a pony because a Miniature Horse is under 38" and your height and the way you look together do not ad up. I would guess she's between 10.3 and 11.2hh? That IS a pony.
B. If she was a Miniature Horse most if not all minis arrived from Shetland breeding, Shetlands are ponies so you'd be dealing with a small pony anyways.
From there no, ponies are not "all bitches" but people put children on them to ride... Take ANY horse and let a kid at it with no adult training and it will develop snotty behaviors as well. Ponies are smart and quick, thus miss under stood more often than not.
And lastly yes, you are to large for the pony your riding in the photos but there are ways around that if "you" want to train her yourself.