The only collapse I see is that it's possible that "I have one girl" would imply ONLY one girl.
BG and GB as possibilities that often collapse in the minds of those thinking about this problem but that is exactly why the problem is paradoxical, why a certain group of people not only get it wrong but also can't let go of their wrong answer.
Another possible collapse would be to say "I have two children, and the oldest [or youngest] is a girl". That would disambiguate GB & BG, by effectively stating I have G? [or ?G]. Then the odds would be 50%.
BG and GB as possibilities that often collapse in the minds of those thinking about this problem but that is exactly why the problem is paradoxical, why a certain group of people not only get it wrong but also can't let go of their wrong answer.