There is no individual babysitter onboard, but the Oceaneers Club/Lab will be open during your dinner time. Last I heard, the Club/Lab was not serving food -- you can verify that once you're onboard. If that's the case, you can get your granddaughter food from the quick-service places on the pool deck or from room service before you go to Palo.
As lklgoodman mentioned, when you drop her off, you should mention to the Club/Lab cast member that you are going to Palo. If she shows an inclination to leave, they will try to keep her engaged for at least the duration of your meal.