They do have rooms with two doubles. We stayed in one last night. I am sure they can accommodate your daughter’s food request. They seem to be very concerned about food allergies as they have everything listed on the menu as far as what’s in the particular dishes.
While there is no direct route from cliff of moher to Cabra castle, you could get a bus from there to Dublin, and from Dublin change bus and travel to Kingscourt. From kingscourt you will have to get a local taxi to Cabra castle _approx 4km away.