irellia mechanics

i have been trying out irellia . i have played in the past with her but left because she was too hard to play and i was relatively new to the game. now 1 year later i can stack properly with her i can pull combos yet i still cant kill enemys. most comon combo i use is R Q E E Q Q auto. but it doesnt work. idk if it is because i am not building tank or if my items are wrong i go for Blade of ruined king, triforce, berserker greaves as my core items yet same results all games even if i change some items.