I would just have them get a regular studio.
When our DD was younger and we could lift her into a tub, we just got a regular room. For a fully accessible room with a roll in shower, it will also include a raised seat toilet, which we found to be a problem when DD was little. Even now, at 5 feet tall, she is too short for her feet to touch the ground, but we need the room with a roll in shower because she is too big to lift in and out of a tub. Another thing we noticed was that as DD got bigger, so did her wheelchair. So she had little difficulty getting around in 'regular' room, even though someone in a full size wheelchair might find it tight.
I have not stayed in a SSR accessible studio, but we have stayed in a 1 bedroom with a roll in shower (we are in one right now) and we have stayed in accessible 2 bedrooms at other DVC resorts. Our room that wr are in right now with a roll in shower is the same general plan as the regular rooms.
The DVC bathrooms are usually big enough that the roll in showers use the same bathroom space as in the non-accessible DVC rooms. So, chances are the space will be arranged almost exactly the same and, if it's not, the bedroom area will be smaller to make room for the roll in shower.