her damage was enough to kill you even though you were blocking ... For example: If you have 10 health left.and her damage would normally do 100 damage unblocked, and 20 damage blocked.Even though you blocked, it still enough to kill you
No this has been discussed before Even dorky diggity Dave made a video about this
I think it may have to do with the crit failure/unlucky/lucky interaction. You holding block triggered it when Blade tries to heal and Domino stopped it with the crit failure. She can do serious damage through blocks like masacre when you're unlucky as well.