Well, I'm a guy, but you mentioned that you were flirting online. It's easy to idealize and obsess over someone online, especially if it's long-distance, because you only get to see filtered information about them. And if we humans like someone/-thing, we tend to fill in the gaps rather optimistically.

But if you then find someone offline, who you can physically hold, and about whom you learn so much more real information, that can quickly feel more serious and more like love.

But yeah, you won't know for sure. Maybe you can ask her about it one day, when the dust has settled and there's ideally a concrete reason for you to not be flirting with her (like either of you being in an official relationship).