How to counter a (fed) Diana?

Hey everyone o/

Im trying to improve my Gameplay against certain Champions, but im stuck against Diana. When i play mid, i just instalock Malzahar wich works fine and dandy. But everytime i play Jungle (my favourite role) and the enemy has a Diana, she will no doubt be fed around the 15 minute Mark. Never had a Game against Diana where my Midlaner managed to win. Playing as Sejuani with over 200 mr and armor, she still manages to one-combo me. I know that CC in general works well against Assasins and All in Champs, but im dead before i can get my E Stacks. Looking forward for your advice :)

Greetings Swizzey