A. First of all, I hope her health state improves. When you are going through various medical treatments you're out of control of the situation and then suddenly become out of control of your beauty situation – it can be a complete nightmare.
As the treatment finishes and the medicine leaves her body, which will be several months, her nails should come back to normal. But in the meantime, I would recommend massaging oil onto the nail as much as possible. She should try OPI's Avoplex oil.
Alternatively, the one that potentially could improve her nails (it can be a little hit and miss because different ingredients work on different people) is Prostrong, the original fluoride kit.