Sara, your story today is far more common than you think, and I think I know why too.
When I was 16, I was on a bus heading for home, dying for a pee and I knew I wasn't going to make it. Worse, I couldn't just get off at the next stop because we had passed the last stop before mine and it was 30 minutes between them. So, I sat there on the back seat and just knew I wasn't going to make it home.
So I made sure I was not sitting on my skirt and kinda just waited for the inevitable. In the end I let a little trickle go and instantly, like throwing a switch, was as horny as a bitch in heat. I felt the wetness spread and all kinds of images flashed into my head. Like the feeling when I get horny and wet, but more so. I let more go and then I just relaxed and let it flow. I couldnt be seen so I spread my legs and rubbed the pee soaked panties and BOY did I CUMMMMM!
Since then I have become a regular panty wetter and have even gotten my best friend into it too. Sometimes we sit astride each other and do it into our panties.
I think its two things. First because when girls get horny, we get wet, being wet down there is kinda automatic turn on, second, well, it's naughty, right? And sometimes its GOOD to be naughty.