Feeds
The 17-year-old was sent home by judge Sir Andrew Lloyd Webber after facing Rachel Tucker in her third sing-off.
Lloyd Webber admired Niamh's performance of 'Another Suitcase in the Hall' from Evita, but felt she may have been too young for the part of Nancy.
He said: "Niamh, if I was casting Evita, I would seriously think of you for that role. Rachel I thought you handled it well, you warmed into the song. Ultimately, tonight I have to save Rachel."
After making the decision, Lloyd Webber told Niamh: "Your voice just needs time to mature and I wouldn't be surprised if you weren't up for a major leading role when you're 20."
Rachel makes up the final four Nancys with Samantha Barks, Jessie Buckley and Jodie Prenger.
From the Oliver hopefuls, 13-year-old Jonny from Warwickshire was chosen to progress to the semi-finals.
