Yes. Go ahead and tell her the first week, which you already have scheduled, is "your pick." That way, if future vacations get canceled, or you don't want to have to plan them well in advance, you won't have to worry about it.
Guaranteed hours mean you pay her anyway if you go away, but the "you pick" week should be something you tell her about at least a month in advance (sooner if you can) so that she can make plans herself.