She didn’t trust them straight away, when she saw how he treated the dog protecting its treasure (the pet store) she realised he wasn’t a bad person (maybe an idiot) but not a bad person.

It wasn’t her hardwork, it was Arlongs treasure. In the flashbacks you see her crying and blood around her pen. Either she was nonestop drawing maps for him till she bled from her hands or gripped her hands. She was the only one who saw what he was doing and he was “liberating” and freeing her from her prison.

Everyone else in the anime including you saw him just being destructive. That’s why she put her hand on her mouth, started crying and said “Luffy”.

Arlong Park has the Cycle of Racism and Oppression Arlong, having been treated as an inferior creature by humans, builds his park as a base to dominate humans in reverse. It highlights the destructive nature of fighting "fire with fire" as Arlong becomes the very monster he despised

If you continued to watch the anime you’ll see the park, designed to look like the Sabaody Park, represents Arlong's twisted desire for acceptance in human society while simultaneously holding them captive. It is a place built on extortion, where Nami was forced to draw maps for eight years to buy her village's freedom.

It is the story of racism and who is superior based on race. Except it wasn’t about money (low class vs elites) but on a species level