It is not clear at all if you have even taken the most basic step -- provide feedback for this employee. It's just not clear how to reconcile this impression -- nothing has been said at all -- with the plea for "rescue" from this situation. You mentioned "personal development", so this is a great opportunity to develop those management skills.

You need to provide feedback for your employee. Have a frank discussion about their performance and try and find out what is the actual problem. Assuming there has been little to no actual conversations, it seems you are merely projecting various ailments here. Maybe their cat died, maybe whatever. We simply do not know.