To what extent is Mayella Ewell in control of her life and her future?

In To Kill a Mockingbird, race and class play important roles in how certain characters are viewed by others and where they exist in the social hierarchy. People of color, for example, are at the bottom of social ladder, but very poor white people are not so far above them in the eyes of the more financially stable people in Maycomb.

Mayella's class status, which is very poor, dictates her options and opportunities. Because she is the eldest women in the Ewell household, she is expected to take care of her father and many brothers and sisters, significantly limiting any free time or opportunity to pursue things like employment or romantic relationships. In simple terms, she is a servant to her father and is more or less shut off from the rest of the world. 

It's important to remember that, while she is indeed lying about being attacked by Tom, she is doing so at the direction of her father. In fact, Mayella can be viewed as one of the more tragic figures in the story because she only lures Tom into the yard because she wants attention and affection from a man, but things escalate once her father finds the two of them.

Like many poor young women in the early part of the 20th century, Mayella has very little control over her life and is almost certain that she has no future outside of the Ewell home.