As Tom's wife, Helen gets to share in the town's persecution of her husband. Fun! After his arrest, she has difficulty finding work, and it's only the concern of Reverend Sykes and the kindness of Link Deas that enable her to support her family. When Ewell harasses her on her way to work for Mr. Deas, she doesn't want her boss to get involved, suggesting that after her experiences with Tom's trial she just wants to attract as little attention as possible, but he does anyway.
Helen's main function in the novel is in relation to Tom: other than making Tom's character more believable and sympathetic, and showing the wide-ranging impact of the Ewells' accusation, she doesn't have much to do.