The 16-year-old singer, who will be mentored by Tulisa Contostavlos if she reaches the Live Shows, is ranked at 11/4 to triumph with Oddschecker.com.
Ella's cover of Cher's 'Believe' at Boot Camp was one of the standout performances from last weekend's shows and was one of the most talked-about moments of the series so far on Twitter.
She overtakes Jahmene Douglas, who has slipped to 6/1, after he struggled to overcome his nerves at Boot Camp.
Elsewhere, Carolynne Poole is well backed in the Overs with odds of 10/1. James Arthur and Kye Sone can be supported at the same odds.
Songwriter Lucy Spraggan is 12/1, while GMD3 are the most highly-rated group at 16/1.
However, the bookies were famously way off with their predictions on last year's show. Eventual winners Little Mix had odds as low as 70/1 before the Live Shows kicked off.
The X Factor Final 12 will be picked on this weekend's Judges' Houses show.
X Factor Final 24 - Photo Gallery
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