Wow.
My first response is, whatever your next lock is, don't let the 5 year old know how to work it.
Whether or not it made some sense to let her have access to the fridge (it doesn't make sense in our family, because our fridge is So Full that noone except me can safely remove things :P ... I hope to acquire a second fridge soon), it doesn't anymore. If she was 'big girl' enough to have access to juice or whatever, she has lost that privilege by not keeping the fridge _shut_--and she MUST know(!) that she has been part of this enormous problem! Five is TOTALLY old enough to understand that and to have (VERY) logical consequences applied: you don't close the fridge, so you don't get to have access. Period.
Oh, I am so sorry you have to deal with this.
Do talk to a doctor, or hopefully someone here will have good advice on fulfilling whatever is the need your three year old has, _without_ doing it the way your three-year-old has discovered herself :(! More baths, with some safe-for-babies bath oil, is the only thing that occurs to me ... redirecting her to an "acceptable' form of the activity, until she grows out of it or you figure out something that is causing her to do it and change the cause ...
God bless, and good luck!