It does seem like Yulia's voice was manipulated ALOT in 200 k/m Per Hour and every song after that her voice has been very raspy. It does have to do with her maturing.
There's this video of Yulia trying to hit the notes and she is nearly on.
http://www.youtube.com/watch?v=_Nm69xgIEeE
Its the only time I've ever heard her sing it live. At 1:32 you faintly hear her try to hit the highest note and not a sound comes out.
If Britney can be one of the most well known singers ever and never sing live I don't think its impossible for Yulia to break into the market. I just don't think shes a strong singer anymore.