Special attention needed so take it to a watch repairer for cleaning, the salt left is probably the problem.
Hairdryer to dry it out don't try repairs yourself you could end up ruining the watch and it sounds expensive with diamonds.
Next if she has a cheap watch, screw back type usually water proof. If she won't wear a cheap watch then stop her going swimming. I used to put a watch in plastic bag fold over the opening then tie it tight. Take a look I came across this on Google search.
Precision Design PD-WSC Waterproof Case Yellow with Neck Strap
Not suitable? then when looking at others ensure they are submersible not just surface water proof (rain).
BOB UK
September 2014
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix wrist watches.