I made a joke that caused a teenage girl to cry.
Like in person? Or online?
I was posting Facebook statuses, and she became sad when I mocked her, but she didn't deserve it.
You should consider how your actions make other people feel. It is not nice to mock people or to tell jokes that make people cry. You should consider apologizing to her.
It was just some stupid joke, so what if I made her cry.
You say she didn't deserve it, but you show no consideration for her feelings. Just apologize, please.