K.I.
I would have just quietly walked over to the sink and washed them off.
If she was a really good friend I would have gone over and grabbed ALL the grapes and washed them off in the kitchen sink and then put them back where they were & then would have told my friend about it.
Sometimes when setting things out for a party you mean to do something and then get distracted, it's entirely possible she had meant to rinse them but just forgot? Even if she didn't intend on washing them its not a big deal...a quick simple rinse in the kitchen sink is not disrespectful or rude, IMO. I could be wrong but no harm no foul, ya know?