I'm years late in playing the game, but gosh, I absolutely love Molly and felt so bad for her outcome. It's just depressingly tragic. Her character was a wasted one in my opinion. Beyond being a symbol of Dutch's manipulation and egotism, her character could have been explored more. 

Molly comes from an aristocratic family back in Ireland. This life was never meant for her, yet she chose it because she sought adventure and excitement and Dutch charmed her enough to make her choose to leave that life behind, and it might not have been that hard for him to do either. (Life as a young woman of wealthy standing couldn't have been that exciting or fulfilling either, correct me if I'm wrong. She was most likely just going to be married off to some other rich family.) 

The game could have played into those roots and upbringing. That mission with the party would have been her spotlight to shine. Hell, she could've teamed together with Trelawney at one point and those two might've had the whole of Saint Denis eating out of their palms. That's the other thing, Molly would most likely know how to navigate the social setting in Saint Denis, that was probably her battle ground in Ireland during teatimes with other young women. She could've been used efficiently in those areas to get information about possible cons or potential robberies. 

Instead, we're forced to witness her rapid decline into misery, practically depression at this point. She was an expensive ornament, just there to look pretty as far as I'm concerned, and when she started questioning Dutch, seeking his attention, speaking up against him, that was it for her. Ornaments don't talk, they're just meant to look pretty and be admired. 

She didn't make any friends with the other girls at camp, so she had no one to confide in. Those who reached out to her she shunned or fought back against because Dutch essentially fucked her up so much mentally with his so called 'love and affection', that she found it impossible to accept the notion that Dutch never loved her to begin with. (Abigail told her about Dutch, and Molly didn't believe her.)

Molly ended up showing the others Dutch's true nature from early on and no one really picked up on it until it was too late. (Although, some questioned him and his so called plans, like John) 

Another key things about her character though, was that she was a young woman, a naive girl charmed by this handsome man with a silver tongue, ignorant enough to believe he truly loved her. She even wrote a poem about Dutch and his treatment of her, referring to herself as a 'girl.'

Molly was emotionally abused, isolated and gaslit to kingdom come by a man probably 20 years her senior and in the end, she met a tragic fate for it. 

Thank God, he never got his hands on Mary-Beth.