Missing: Accent. If found....

[Afrobean]

Accents fade with time and people often pick up new accents.

In this case, it was probably just a case of her being relatively poor with the accent to begin with, so she ended up dropping it as her speaking part grew in the sequels. It is easily explainable though, so it doesn't bother me.

I mean, does the film continuity even establish a reason for her to have an accent anyway? Not a big deal, folks. It's not like they went out of their way to point out and establish a history of her having grown up in Africa or something.