Assuming you are an American, what is your sick day policy? Does she have to use vacation time to stay home when sick? How much vacation time does she have?
I'm not American, thus, using vacation time as sick leave is illegal. However, what really aggravates the crust of all of this for me is the fact that my manager would be 100% ok if she asked him if she could WFH while she's sick -he's allowed other people to do this before, but nobody is gonna force her to.