I had a boarder's horse do a similar thing this spring with his hind leg. We still have no clue, some pasture freak accident.
We had my vet come out right when I found him. Our story goes like this:(time frame maybe a little off)
He came out and stitched the wound closed with a drain. We had him on penicillin twice daily along with but and stall rest. We also put pillow wraps and standing bandages on him to aid with swelling and support. Bandage changes happened twice daily for first 2 weeks. And he was on stall rest. Along with bute 2x day. We used a slave for bandage changes called nitro something (i forget the the name). He was knuckling over the toe and would drag.
Around the 3-4 week period a few stitches have been ripped as the tightness with skin. The wound was about a fist size big. So the vet pulled the drain out and we continued with bandage changes now once a day and switched him over to a oral antibiotic twice daily and lowered the dosage of bute 2x daily.
Around 3 months we had the vet come out again. We took him off antibiotics and put in some very loose stitches to promote skin growth in the verticle direction. We were given the okay to turn him out for few hours a day by himself. But we kept him wrapped. Other than the stitches we did not see much new skin growth yet.
At about 4 months the vet came out and pulled the loose stitches. He was amazed with the progress and the pink new flesh. The knuckling over the toe has ended. We where than given the okay to turn him and increase turn out time.
At about 5 months he was back in his herd, with bandages. At this point we just wrapped the lower leg with a maxi pad and standing bandage for support. The would closed even further.
The wound has pretty much closed now and we tried leaving the bandages off, however about 20 mins later he balloons up in the lower leg. With the bandages on he would gallop in the pasture buck and kick. We had the vet out to do teeth and he took a quick look, and this is where we are today.
The vet explained, he can't replace blood vessels which is true, so now it's waiting on him to adapt and retrain to take blood supply back up. So we are now wrapping back with a pillow wrap and standing bandage loosly to slow down the blood flow and let things work their way out. We have been okay to start him back into training (he 4) with polos on the back leg.
By your pics I would not be turning her out with an open wound like that unwrap. Also to me looks like some proud flesh is starting. I know with my boarders horse there was no proud flesh.
I also had a paint do a simular thing with his hind leg on a trailer. He missed the tendon, but I did simuilar as above and it took about 5 months to heal, although he didn't have stitches. Today he sound and happy.