The nursery is for children 0-3, so they have a lot of things to entertain three year olds so she shouldn't get bored, yes theres lots of baby things, but there's also toys and activities for older children: dolls, little trike things, balls and nets, a mini side, painting, colouring, play doh, movies, books...and characters often come and visit too.
Occasionally, if the nursery is quiet, I have seen nursery children go into the club with a nursery counsellor if that option is available.
However, as long as she's not in a pull-up/ diaper, she can go into the club lab. Any adult authorised to pick her up can come in and check on her and take her to the family bathroom together. Counsellors cannot help children in the bathroom, and if she does have an accident, then the kids club will call you.
(I think) all ships now offer something called pre-school fun which is just for 3-5 year olds. Its quieter and calmer and aimed at the younger children, just for an hour or so. As counsellors we're well trained in spotting the 'Potty Dance', and its a lot more noticeable in this environment.