She’s doing half of the high five, you’re doing the other half. So what should you do if you find that annoying? Well, then don’t do it! Don’t do the other half, don’t raise your hand, and that’s it.

She’s doing that and it’s annoying to you, because a high five is opposing you and your girlfriend, by opposing your body to your girlfriend’s body. That’s why a high five is mostly a guy gesture, not a couple gesture, so if you think that is inappropriate in a couple, it really is, so I fully agree.

If she wants all the time to oppose your bodies, then your couple won’t last, I’m afraid. Then talk to her about that, a hug is really more appropriate.