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This would be an ideal moment for some aquatic transformation. Traditional fish-like mermaids are the obvious option, but maybe the other two girls become whale-, eel-, ray-, squid-, or octopus-like.
Land mobility will be an obvious concern afterwards, so it might be accompanied with Dorothy rearranging the mansion so that everything is underwater. The pool is suddenly on the top floor with a swimmable "river" leading down into the hallways, the garden is now a kelp forest, all the electrical devices are still around but magically sealed, maybe the kitchen only serves seafood...
Hmm. It's something to consider, though it's not what I intended to write tonight. But it can definitely be continued in that direction with the appropriate option.