my mom's mare had a VERY similar wound, what happened was is we had to seperate our herd into 2 pastures, and apparently her friend was in the other herd, some guy put up barbed wire where she kept getting out.. (furiates me to this day!) and she went to escape and got her foot caught, instead of standing still she almost sawed her foot off on the barbed wire. someone found her and wrapped her leg in a shirt and stalled her for us until we could get there. we had to wrap it, and boot it. but we used a DMSO mixture for it and it was healed up in 6 months she is completely sound, the vet had to remove proud flesh about 3 times. and her foot and hoof is a little wonky shaped now. but she is sound and luckily didn't cut anything to serious, her injury was in about the same place as yours, however it was a little more to the back then on the side
i hope she heals up nicely! keep us updated!
Baby, Sparta, Carmen, Henry, Hooch, Mercedes, Butterscotch