After date. Signs that she is still interested? Seriously?

[gurt slap]

Germans have special receptors built into their nostrils which pick up the scent of men who are trying too hard. They are very sensitive, and overpowering them can lead to feelings of nausea, which is probably what happened in your case. Once you remove the source of stimulation (ie. you) the German person will start to feel better very quickly, which would explain how she was able to go out with her friends soon after.

I would recommend not trying so hard with her. Cheap aftershave gives them headaches as well, perhaps this was a factor.