She sounds nearly toilet trained which is great! I would not even go pullups, they are nappies and are thinner and have a liner which tells the child they are wet, there are no tabs so they look more like undies but undo at the side. We tried that avenue and it has led us back to not being TT at all

I would tell them that she will be wearing undies. Or speak to the director of the centre mention the twins and say that your child is up that stage.

Goodluck!