I would deworm and delouse her and put her with your youngest ones. She needs chicken company. Young ones will accept her and she is unlikely to bully them being a lone hen. You could put her in a dog cage inside the run for a few days first if you wanted to be extra cautious. She has already been effectively quarantining on your porch.
She may just be looking scruffy due to molting and poor diet.
She may just be looking scruffy due to molting and poor diet.