After meeting up with Xa, she immediately asked Rein about his strength and how powerful he and his partners actually were. After accepting Rein as a friend Xa did not want to lie to him or deceive him in any way, so she immediately told him about the item her teacher had and explained why she was asking this question.
Even Rein was a bit surprised to see how honest Xa actually was. Rein had guessed that she was an honest and earnest person and that was the reason why he wanted to become friends with her. But even he had not expected her to be so honest.
To not shame her honesty, Rein also told her about their power level properly. He explained to her the power scaling system he had created for the people above the power level of normal power scaling.