I am also lactose intorlerant.
When I was on the Wonder they did not have lactose free milk, but our Head waiter PJ was wonderful will all my restrictions.
He was very attentive and knew all the dishes that I needed to avoid.
Be happy they have ice cream, call rice dream, on board that is great. Only available in the main dinning rooms, but it was excellent.
If you can pick up some lactose free milk, I am sure that they might be able to treat it like other's wine and bring it from restaurant to restaurant for your daughter. You could also store some in the cooler in your stateroom. Dave's site lists some grocery stores near the port.