Maybe it was Meryl! I guess we'll never know. I loved the Moira Kelly interview!
I am also a big fan of: Phantom of the Opera, High School Musical, Harry Potter, Disney in general, Days of Our Lives, musicals in general, Dr. Seuss in general and the Grinch.
"Sometimes, it's better not to say anything."- Speak, by Laurie Halse Anderson
Even though I read that Moira Kelly interview a long time ago, I have never heard of this "original Nala" story. But since Ms. Kelly mentioned the directors heard "different voices" for Nala before choosing her, I decided to go back to look at the deleted scenes cut from the final movie.
I can only assume the actress voicing Nala below in the alternate deleted scene, "Simba Decides to Return", is the "original Nala":
And now, the voice of Nala in this deleted scene below, where Scar tries to seduce Nala into becoming his queen, sounds the same as the voice in the deleted scene above. So, I speculate the actress voicing Nala in this deleted clips could be the "original Nala".
The original voice actor probably wasn't a "big name" so I'd doubt we'll know unless one of the producers gives a name. As a side note, I had never seen the deleted scene for "The Madness of King Scar" before, but now I wish that they had left it in the movie. Not only does it give a better backstory to Nala eventually finding Simba, Zazu is awesome in it.
Come death. Come suffering. I will not live in fear. In this fleeting life where time escapes us, the path of least resistance is a slow quiet death. I'd rather burn out than fade away.