​How to keep employee busy during slow time

In my business I hired a new employee in a semi-management position. What recommendations do you have for handling slow times? When I mean slow I mean rather than a normal 40 hour work it could turn in to a 30 hour week. This employee is salaried so there is no impact to their pay. Any suggestions? There is plenty of work for her subordinates it is her position that is slow.

I came back and edited this post because I think my question really is – is it ok to just tell her to enjoy the slow time? In other words do I “need” to keep her busy?