Meh, you really wanna know who Sheryl is!?
Remember how Sheryl said in one of her blog posts about hearing a singer who inspired her and feeling a form of wind coming from that singer. That actually occured some years back on the bridge of a Metran ship that just got penetrated by a large speaker pod! Yep, Sheryl is actually a micronized Chlore who was inspired by Basara to become a singer on her own right. Unfortunately, she has the same genetic condition as Klan, meaning she had to wait for her micron form to grow up before she could launch her career (which also turned into a convenient cover up of who she really was).
Hey, at least it's better (IMHO) than VFTF1's theory that Sheryl is really Honey Suzuki!