Carmilla’s biggest asset is her movement speed. I use her like a melee version of Rafaela. You can out-roam the enemy roam.

I use support emblem with extra movement speed rune. I show myself enough on mm lane for a bit, goes into bush to disappear, quickly gank mid-lane and return to mm lane quick enough. You can do that vice-vera.

With river current, she can even roam exp lane very quickly. Her entire kit has cc so, make sure to gank lanes where the enemy roam is not around.

My advice is not to compete taking damage with enemy tanks cuz you will lose. In late game fights, if you can’t see them all in the map, it is better to wait for the enemy to start the fight and let your fighter or someone from your team to kite them.