Scarlet is just attacking Lion’s Arch to gather all her adversaries away from her real target. Scarlet’s upfront assaults have all been covers to an ulterior motive. She went through a lot of trouble to make an extremely potent poison, but is sending all her foot soldier fodder into Lion’s Arch to keep us distracted.
The target could be anything really, but I’d bet on the Pale Tree, given that she’s named herself Scarlet Briar after seeing the Pale Tree strangled by red thorns. And the pictures in her hideout. But she’s crazier than a bag of cats so it could be she just really doesn’t like the fountain.
Just a thought.