This isn't all that unusal. When my youngest son was in first grade, I came home from work to find him and his dad waiting for me. His dad said "Tell your mom what you did". He looked down and said he was sent to the principals office and that he had peed in the tires on the playground. Ok, so I couldn't laugh even if I wanted too with the look on his face. I asked "how did you get caught?" He said "some first grade boys told on me" I said "well if the first grade boys seen you do it, don't you think that the first grade girls could have seen you too?" He looked totally horrified at that idea. The principal told me that he made him go out with a bucket and a scrub brush and that he had to clean it up. Then he wasn't allowed to play on the tires for a while.
With your daughter, making her help clean it up is a good thing. To threaten to take her toys away is not. Instead of that ask if she would want someone to pee on her toys don't threaten too, just ask what she would think. She will say "no" of course and ask her why she wouldn't like that. She will probably say that would be yucky.. if she doesn't know say "that would be yucky wouldn't it?" Then explain that her going potty in places that isn't a toilet is yucky too. This may backfire if she is ever camping and needs to go outside if you camp. Most of all relax, it is a phase.