was she vaccinated for Mareks disease when she was a chick? is it her entire body or just one side? is she eating and drinking?....be sure to put a little cup of food and water near her and the chicks. if she cant get around at all, prepare a brooder for the chicks.
Mites are common and Ive found them to be worse in the NE this year because of the crazy weather and so much rain. I would probably use poultry dust rather than sevin around the chicks; I reserve sevin for really resistant cases of mites.
It is common for mites to attack a weak chicken, and it comes on really quickly. If they cant dustbath or move, then all sorts of things can happen seemingly overnight.
I just had a little roo who suddenly got mareks or something like it and was limping around...next thing I knew he was covered with mites, poor guy!
He lay in the coop and could raise only his head and shoulders to eat and drink. I kept him fed and watered, but he died within a week....I had eradicated the mites as soon as I saw them and Im checking my broodys, and discouraging broodiness in general this year...but if you have more broodys, make sure they are getting up and that they arent harboring any mites.
Keep putting DE and poultry dust in the dust baths and around the coop. wear a mask when you do it! you could also try some pour on eprinex.
The paralysis could be from many things. Around here its generally in unvaccinated chickens. Mareks is everywhere so its best to get vaccinated chicks and vaccinated incubator ones.
I would contact your state vet extension and have her necropsied to see what it was...doesnt sound like she will be taking care of the chicks, and the other birds might hurt them. so get either all of them into a rabbit cage or dog crate, or take the babies into a brooder.
sorry that you have to go through this....mites on a rundown bird are the worst! good luck!