After an appearance on Family Ties, O'Neill won the role of the pregnant teenager Molly Stark on the daytime soap, The Young and the Restless for thirty episodes in 1986.

She continued working in television series such as Room for Romance, The Young Riders, and Gabriel's Fire, and starred as Susan Hartley in an episode of Murder, She Wrote.

The reason for this is that the film was originally a standalone story unrelated to Honey, I Shrunk the Kids, and when the plot was changed to include the Szalinski family, there was no parallel character for O'Neill to replace.

O'Neill later appeared in the television film, White Wolves: A Cry in the Wild II as Pandra, one of the young adults stuck in the Cascade Mountains, having to fend for themselves.

As of 2023[update], O'Neill was working to produce a film tentatively titled Burn Down the Night, based on the 1982 book of the same name by Craig Strete, about the life of Jim Morrison before he joined The Doors.