Wasn't the answer to her not mentioned in ROTS simply the fact that (Spoilers) left the order?
On her role in the saga I recommend the following read;
** Source; Article
Has any one heard of the term..... lazy writing. She wasnt mentioned in ROTS or ANY media before hand was because she wasnt invented until people wanted to milk more money. Thus they shoe horned her in and then swept it under the rug and pretended like she was their the whole time and they just didnt mention her cus it wasnt relavent.
People are making excuses for a bad writing team and concept team
Like I said what they eventually do with her is good, because it went from lazy and bad concept to people picking up the peices and actually giving 2 cruds and making it work. Doesnt make the idea any less bad