Horse Sheet Size

As you know, fly season has begun. I've just bought my horse a fly sheet for out in the paddock. The thing with my horse is that she has scar (that she's had for 8 years) about the size of a toonie on her hip. I've constructed large flap on her fly blanket where her scar is so that the scar won't chafe and it won't sunburn. The problem is, it's still chaffeing and it's always red and bleeding. Is there some other way I could fix her blanket or anyway so stop it chaffeing?