Susan peed on her sweater.
She got it a number of years ago from one of those clothing stores that sell everything for $10. It's probably lasted so long because it's ninety percent synthetic.
Byproduct of petroleum.
Susan's sweater is nubby and long with a hood that used to have a pom pom until she cut it off. It's used as a bathrobe, as blanket, and as something she actually wears outside the house, but that's rare.

The other morning Susan got up, and since she won't turn the heat on the house was freezing. She put on her petroleum byproduct sweater and went to the potty. While she was sitting there she had time to consider whether she had gotten her sweater completely out of the line of fire. She's had tons of experience wearing the sweater to the toilet so she felt confident that everything was fine. She concluded her business and as she was turning toward the sink she realized that she had miscalculated the ratio of synthetic nubbyness to toilet seat circumference to urine stream trajectory.
She had peed on it.