Thanks for your invaluable comments!
BMC, your advice to use serve as a guide makes sense to me. I think I won't let her compete before she can master that well enough.
That "make the other girl cry" stuff...well, that made me wonder also...So I asked her if she could explain why she'd like that and for an answer she mumbled something like 'I want my opponent to really feel my good game'
I think it may have something to do with our practise habits where, besides spending majority of time learning the right technique, I make her play points with her brother so that there's either some 'prize' for the winner but even more often some appropriate "humiliation" reserved for the loser - like singing loudly some (stupid) popsong while jogging around the park (which 'punisment' she and her brother have always decided together) ...
But I'd be more than happy to hear more (following #1 coach) of your ideas how to raise a kid with a mindset of a winner?