A recommendation often given for fixing soups that have been oversalted is to add some potato. Supposedly, the potato will "suck up" some of the saltiness. Unfortunately, food scientists have proven this as just an urban myth. While the potato may taste salty, the soup is still just as salty as it was before.
Sooo... I can see where the advice is coming from. (You can decide whether or not to tell your girlfriend that the potato reducing saltiness thing is just a myth!)
Even if it DID work... sure seems safer to just take some salt water out and put some RO
water back in! Slowly... of course, as to not change the salinity too quick!