I believe this is fake until there's actually a trustworthy source.
However, Erika would already be a better choice than what Tsunku might pick from auditions. 1.) She's already 15,
2.) she has a cute, nice voice (much better than Koharu to begin with),
3.) she has lots of experience already,
4.) she only keeps getting prettier as opposed to looking pretty scary a while ago.
As long as she wasn't the only new member, I would be completely ok with this.