OK now I have a weird potty situation

Chloe goes on potty pads and Sydney goes outside...well tonight Sydney seemed to realize that Chloe doesn't have to leave the house to pee...so Sydney walks over and pees on Chloe's potty pad
Well when Chloe pees it's a small amount being she's so tiny...but Sydney is 10 lbs. so she left a hugh pee spot and then Chloe wouldn't get on the pad with Sydney's pee on it...( can't blame her there)
SO ....how do I train a dog not to use a potty pad when her sister is


Oh Lordy , just when its going good...
hopefully it was just a one time " I have to pee so bad I can't wait " deal on Syd's part. She has never tried to use a potty pad and never showed any intrest in Chloe's pad till tonight. She's been trained to potty outside for years and it's like she just went..."hey , why does SHE get to pee in the house?"
Good luck everyone...Thor and Nikko sound like they are doing really well