Against evelynn, Evelynn’s early game is very weak and she will be power farming till level 6 so she can become invisible and get her Ultimate R. Try and invade her jungle and steal away her camps to delay her level 6 power spike. 

Place Control Wards in the river and go for deeper wards rather than relying on shallow ones. This will help you spot her before she gets the chance to become invisible. Placing wards on her camps are a good way to counter her.

Evelynn wants to assassinate targets that are alone. Group as a team to make it harder for her to execute and kill squishy champions. Against evelynn, Evelynn's beginning game is very weak and it will be the power farming up to level 6 so that it can become invisible and get its Ultimate R. Try to invade its jungle and steal its camps to delay its level 6 peak power. Control Wards place in the river and go to deeper rooms rather than rely on shallow areas. This will help you to spot it before it has the chance to become invisible.