@Simran my take is this. Gayatri is alone at this point. She needs to create allies. And kitchen and food is the first point to create allies. I mean she has to prove herself before the king can trust her with her policies on the kingdom.
See here King-Queen trust factor doesn't exist. To build trust it is always better to start from a place you are familiar with. Gayatri might know the way kitchen works as Gopal Seth told. I have given education to her to be a good house wife. So kitchen and other areas are familiar to the girl. She was not trained to be a Queen.
Once she gets done with her familiar area with RMs guidance she should move outside. I would say here role of RM is very very important as she is going to be the mentor for the girl to step out of the comfort zone.
And yes I am fine starting of with Kitchen, but I am not fine keeping her in kitchen and other domesticated areas. She has to start moving around.