Ella Enchanted follows the grand tradition of naming books after the main character (think Jane Eyre and Oliver Twist).
However, since it's not just called "Ella," we have to assume that the "Enchanted" portion of the title is also significant. Why might that be?
Oh, hang on, we've got this one: because the spell on Ella is one of the main determining factors in how her life goes. For one thing, it makes her into a rebel, since she feels like she's gotta fight against every command she's given or else be a total puppet.
The "Enchanted" stuff really impacts Ella when the narrative kicks off and her life gets unsettled. Up until her mother's death, she lives a relatively sheltered life and doesn't come into contact with many people who might learn about or abuse her curse. But after her mother's death, everything changes: she meets repulsive characters like Dame Olga and Hattie, who use the spell to oppress her, while she also encounters wonderful people like Char and various people from magical races.
In dealing with the "Enchanted" part of her life—which requires rising about her stepfamily's petty crap and putting others before herself—Ella proves her strength and compassion again and again. So, the "Enchanted" part of her life makes her stronger, even though it also makes her suffer. In other words—it makes her grow up.