I agree, she gets KR for sure, just less than Chara would.
and yeah the dice thing depends on if Sans can find someway or loophole within the odds to make it so they don't fall or gets lucky and is able to destroy them or stop them somehow, but Vriska has the power of Luck on her side
Sans may be good at reading people and making guesses basd on his perception, but has no way of knowing 100% for sure, for him, its still a chance he could be wrong and he can be wrong about stuff like that. Remember in the diner when he straight up says to the kid "and you havent died a single time" or something like that, and its only after he sees your face that he guesses he might be wrong
Its still a chancy thing, despite its accuracy, and if theres chance involved id say Vriska wins the coin flip
- edit* not to mention eyes, seeing and perception all are powers that fall under Light anyway, so Vriska could even make it so Sans can't percieve or make guesses based on what shes about to do, by stealing it away from him