Welcome. I am so sorry for the loss of your brother. Thank you for taking his flock. I am most certain you are dealing with fowl pox. Here is a link: https://www.poultrydvm.com/condition/fowl-pox
Very sorry about your brother. And sorry you're having to deal with perhaps an ill chicken of his. Hopefully, with the links and information provided above, you'll get her past this. If you need further help down the road with this, be sure to post it in our ER forum.