When playing Vivian note that you can cancel your shield, I see lower level players keep it up when they aren't using it which means they have to wait longer to be able to use it again.
Vivian's shield only protects in front of her, use a flank champion such as Skye to attack her from behind. With any champion you should still try to attack her if doesn't notice you.
If Vivian uses her shield, aim for her feet if you’re running direct damage, or the ground below her if you have AoE. This is extremely useful in any range combat with her.