I expected to see proud flesh but there doesn't appear to be any, nor does she look like she's fighting cellulitis
My thought is she is dealing with Scratches, a/k/a mud fever and is having a difficult time getting it under control because:
1. Her immune system is weak
2. Leading her old injury to be compromised, making it easy for the Scratches to take hold.
She is probably a candidate for a dose of Liquid Vitamin A. I am not well versed on dosages because it's something you have to do carefully and I never have.
Hopefully somebody will come in with the formula of how much and how often.
By "vitamin A", I mean the injectable Vit A used on cattle, except it is given orally in horses
I don't see anything life threatening and it's relief to not see proud flesh, I just think it's going to take a lot of time & topical treatment, a healthy low starch diet and some Vitamin A