Most of Willo's kit relies on area denial. After Seedling or Dead Zone have been used, it's better to stay out of reach. Remember that she has quite a large cooldown for those abilities!
Lex has the loudest footsteps in the game. Turning off music and using good headphones might help you pinpoint his current position if he's behind a wall.
Slither cancels Hunter's Mark. Giving your position as a healer is bad, so it may be a good idea to slither away to get rid of it. You can still heal your teammates from a distance!