How to ask her to be my official girlfriend online

I joined a romantic tours international event last year and I think I met the girl of my dreams. Since then, we have been in constant communication with the help of the internet. We use instant messaging apps from time to time. However, our setup does not seem to be official or exclusive. I want to make her my official girlfriend as soon as possible.

As much as I want to ask her to be my girlfriend in person, we canít personally meet each other anytime soon. Would it be okay if Iíll ask her to be officially mine online? And if itís okay, how should I do it? Should it be casual or should it be special? I know this is not yet even close to a marriage proposal but I really want her to feel special and I want both of us to agree on dating each other exclusively.