You might think it is normal for you as you have the habit, but I know plenty of people that do not give handshakes or any form of physical contact. So it is a possibility that she might find it awkward and unnecessary, and so it catches her off guard. As others pointed out, thinking about why that happens is pointless and though you might wonder this to be thoughtful, it’s better to just wait for her to raise the hand instead of you. If she does not, then there’s no need.

Proud of you. Now going for an all-technocratic party game?