I haven't had to deal with mites but I know the wood ash helps get rid of them. Haven't ever used seven so I can't speak to that but a lot of people here do...
I would leave that alone and just keep an eye on it.
If you are seeing pin feathers, she is most likely just molting. Probably why she is being grumpy with the other hens. It's not comfortable for them and they get grouchy...
If she is sick, the best thing for her would be to separate her until she is better. If she is not getting along with her flock at the moment, the stress will make it harder for her to make a full recovery.
What symptoms is she still having?
You could also try adding wood ash to their dust bathing spots. If you have a fire pit where you burn wood or maybe someone you know does, you can gather the ash from there. If you suspect they have mites (I don't know how well it works on SLM though) you can actually rub it directly on them...