Nicole's voice isn't suited for melodic, soulful Motown songs.
Her voice wasn't supported, making her high notes sound shrill.
Had she been trained, she'd NEVER sing high notes with her head held back like that.It takes the voice box "out of the breath", as some call it. The preferred technique for hitting high notes is called "lift & tip", where the chest is lifted & the chin is tipped slightly. This, along with diaphragmatic breathing & lower abdominal contraction will give the high notes fullness & resonance.

Here's a clip of how a truly classically trained pop/jazz singer hits-and sustains-high notes-in her 60s:
http://www.youtube.com/watch?v=-vOrILQS0Hc
(Sarah Vaughan, performing "Send In The Clowns"-LIVE)
Yes, Sarah Vaughan is a LEGEND, but, unless the new crop can create the kinds of magic created by the legends, the superlatives heaped upon chicks like Nicole is just hyperbole of the worst kind.

That marginal "singers" like Nicole constantly brag about being classically trained just demonstrates how many poorly-trained voice teachers there are out there, taking advantage of the ignorance of their students.