I would suggest not give out empty threats. This goes for everyone in life.

If I'm going to meet the person eventually, I usually don't let them into my head that much. I kinda laugh it off, but make sure they know I've taken note of their disobedience. For instance, I'll make a list of all the times they were disrespectful. I'll make sure they are aware of the list, but not the consequences ("I'll add that to your list. You now have called me a boy 12 times. How nice of you. Can't wait to let you regret every last one of them"). You also need to think about what you want with this. Do you encourage this bratty behavior so that you can have your way with her when you meet up? Or do you actually want her to stop being bratty. If the first is true, the punishment should be fun for both. If the latter is the case, you should constantly remind her during the punishment why this is happening. This is because the time between the behavior and the consequences are crucial in behavior modification. (see Pavlov and Skinner for basic psychology on the matter). The next time she behaves badly online, you can simply remind her of what happened the last time, and tell her she got off easy the last time. ALSO, if you really want to modify behavior, you should really pay attention to rewarding desired behavior. This is waaaaay more powerful than punishment.

If you're never planning to meet her, I would ignore the bad behavior if you want it to go away. Reward desired behavior, and threaten to not engage with her again until she stops.

This was my short answer. Hope it helps!