How much soda does she actually drink? If it's only a couple a day, and the rest of the time she's okay with juice and water, then I'd just suggest having her buy soda a la cart on board. It'd probably be like $10 a day for 3 sodas, and she can get some juices and water for free on the lido deck.
As far as wifi goes, as people have said, it's not bound to any person. Your family will be able to connect 2 devices at once, and the devices can change. I suggest letting her have the wifi for one of those devices full time, and you and your husband can alternate the other wifi connection.