Against diana, When she is low on mana, she is not a threat to you as her kit requires a lot of mana to trade effectively. When she’s low, there’s your chance to fight.
 
During team fights, Diana's kit offers a lot of burst damage thanks to her Ultimate R. Try to poke her down before she engages to make it really hard for her to engage and kill anybody.
 
Diana's engage is pretty scripted. Ward to the side when sieging an objective so she cannot surprise your team with an all-in Against diana, When it's weak in mana, it's not a threat to you because its kit requires a lot of mana to trade effectively. When it's weak, there's your chance to fight. During team fights, Diana's kit offers a lot of brilliant damage thanks to its Ultimate R. Try to bring it down before it engages to make it really difficult for her to engage and kill anyone.