Counting traits for potential

[Bea Shamrock]

I think you're right -there's a 50/50 chance mum passed Twinkle, but no way of knowing until you breed the kitty, if I got it right: Mum's dad shows Twinkle, everyone else porcelain. If so, mum hides twinkle and shows porcelain, so she could have passed twinkle and your kitty have it as the hidden shade. Or mum could have passed her shown porcelain and your kitty is both showing and hiding porcelain, since there's no in-between shade.