Your location sais 'amsterdam,' so I'll assume you're living in the Netherlands. I don't exactly know how far Dutch law goes, but after that XS4ALL refusal to hand over customer-information to the authorities, and the lawsuit following that, Dutch gouvernment has passed a law making it easier for the police to gather information about you from your ISP.

Freedom of speech isn't that pressed here as it is in the United States. If youu want to know exactly what you can expect, you'd probably need to see a lawyer. Best is you apologise to the girl in person, though. If you're going to seek legal counsil, you might be sending out a message that you're willing to fight this in court...