She's trying to explain Mio's condition in a respectful way that is also easy for Kurose to comprehend and understand. She's also at least somewhat aware that Kurose himself is currently in a fragile place mentally. If she told him to go see her, he obviously would. But then it would be perceived as obligation, especially by someone dealing with a low point of their depression. Not to mention that pushing that responsibility and obligation onto Kurose is incredibly unfair, even if by all accounts he would be entirely willing to take it on.
Telling him about Mio's struggles but also conveying to him hopeful prospects makes it clear that he has value to Mio, that none of this is his fault, and that he does and can help Mio with his presence. It also gives him the space and the agency to process all of this information before coming to a decision for himself on his own terms. Which is also what's the best for Mio, too; when Kurose visits it will be entirely of his own free will, without any sort of imposition from an adult or other authority figure. But if he were also to let Mio have her space and "recharge" at her own speed before eventually returning to school on her own terms, that would also be a valid course of action.
Depression is a bitch partly because how it affects people varies from person to person, as does how they handle it and how well they're able to. There is no one single "always right" answer when it comes to depression or how to help someone work through it.
