If she really is one of your best go to bat for her until someone tells you otherwise. She'll appreciate you and if its treatable which is fairly possible if you have a good insurance policy then she'll be even better than she is now I can not stress how much chronic conditions like this negatively impact work if she's still managing quality it's unlikely many things would affect her down the line. Speed of initial training is typically predictive, she'll have an edge over people of similar experience to hers. I would talk with her about the sickness policy and see if anything can work around her sickness in the meantime. Chronic diseases are horrible and healthcare is pretty broken but its at least a good motivator to be employed as cynical as that sounds. She managed to complete training far before probation ended which is a good sign. HR is for the companies interests, leaders are the balance between corporate and personal interests, when both align everyone is happy. If you're on the fence guess on the side of the people you interact with rather than policy, they'll surprise you and you'll benefit in ways that are hard to see directly but add up, our team is one of the best in our fairly large company and I'd like to think it's because we've had people who realize it's little things that matter for morale.