There has never been a public restroom that Candle has ever found to her standards. They are filthy and she would rather just go home than use one. It is almost a source of stubborn pride for her.
She is driving around and is desperate to pee but nowhere near her house. She squirms in her seat and struggles to get into a position that relieves her growing bulge of a bladder. After trying to hold it and getting very uncomfortable she decides she is just going to get out of the car and let the urine flow down her jeans clad legs. She knows she is being ridiculous and laughs at herself because there is a public bathroom across the street.
She tries to clean up her wet self, but the best she can do is to grab a plastic bag and cover her car seat. She smiles and with a sigh of relief heads on her merry way.