I have no problems pushing a case on her now that I know Iffrita targetted UK. Anyway, probability.
With 11 players, there are 10 players that could be scum (since I'm town). 3 of them are scum. Thus, 3/10.
If I know player X did not perform the night kill, then X is not scum A. He can only be scum B or C. Thus, scum A is one of the other 10. Thus, the odds of X being scum is reduced to 2/9, which means I should go after the other targets that still have about a 3/10 chance of being scum instead.