Well, partially, the ability was given to her when she was given the disease by Galaxy in the first place, so in a sense, yes it was "artificially" introduced into her way before ranka came into the picture. which makes me think that the movie will tend to focus a bit on galaxy's attempt to make Sheryl a weapon/link against the vajra.
On the other hand, if the "False Diva" is referring to Sheryl's career as a pop diva being "fabricated" by grace.... well, in reality, whose isn't? (yes, i'm pointing at you American Idol! ) if you think about it, even ranka's rise to fame was somewhat manipulated.