If they already put the Plan B location in the invite information then if it's raining you can just go to indoor location.If weather is questionalbe, someone from the wedding party, family or someone else designated should be contacting the guests the morning of or the day before if location site changes. If you don't hear anything and you're unsure, the best thing you can do is leave extra early to allow extra time to go from outdoor location to indoor location. Make sure to check your email frequently that day & if they have a wedding website, that might be another way they post updates. But you are right, best thing is not to call and bother the bride or her family the day of the wedding. Unless they've said, call this number for updates on the cermony location.Good luck to her & hope the weather holds out.