She uses to poor dialogue and her story seems to not serve a purpose she is derided. (There's a whole racial and gender component with her being the first Vietnamese/Asian woman in star wars and that bugging small minded people)

In honestly though it's silly if you think about it. She is there for a few reasons. To show a human (not the species) side of things for the resistance in a few ways

She loses her sister in the opening act.

She shows heros aren't always what they seem.

She's integral in Finn moving from caring about himself or the people around him to caring about the Galaxy at large.

And albeit really poorly executed she falls for Finn. I almost feel like Johnson threw that in there because the Rey and Kylo connection or "romance" feels forced. (Even though rose and Finn feels even more forced)