This puts you in a terrible spot. I think I'd probably do something like you did (send her home but pay her for today) but for additional days I'd simply say I can't pay her.
This is a tough thing but it isn't all that different than nannies asking for loans. In allowing her to use all of her leave you (and she of course) were rolling the dice.
This is why some companies give PTO and some give sick/vacation. I believe in sick leave, but I believe that it should only be used for illness (or care for sick family members, doctor visits, etc...)
It's a painful lesson but I think you're within your rights to not have her jeapordizing your families health, and not paying her.
Really tough spot for you though.
