It's pretty clear from contemporary observer after contemporary observer that Fritz, even Old Fritz, had his charismatic/magnetic side, and that if he wanted to charm you into liking him after one encounter, he could (presuming you didn't already have a reason to be dead set against liking him).

Now, how much irritated must her future husband the ultimate Fritz fanboy have been that she was the one who actually met his hero?

Haha, yup. The Ekaterina series (which really captures the irrational fanboy aspect), has this exchange between them shortly after they meet:

Ekaterina: My father is a general in King Frederick's army-
Pyotr: *I'm* the one who should be a general in King Frederick's army!
Pyotr: *proceeds to make it really clear why Frederick would never have him as a general in his army*