Looking at previous chapters, I don't think it's a contradiction because there hasn't been any other one. And no, don't try to bring the Nabeshima one!
The way I look at the situation, it can be because it's her big sis, and she said she would believe her no matter what nonetheless, or maybe as a result of the many times she has been called abnormal... I will go for the first one, big sis influence.
And sorry for the doublepost, but while in the middle of this discussion that goes nowhere, the new raw is already out:
http://www.raw-paradise.com/
Whoever said Nishio would do 1 vs 1, WRONG.