Is AUTHOR wrong in the post ? POST : A few months ago, a girl came up to me and made me aware that apparently my brother had sent unsolicited dic picks to at least one girl and considering I dont have the highest view of my brother, I didn't question it. Apparently, it was even posted on a group chat. 

A few months have past, an my mother finally figured it out. However, upon questioning, this girl has 1) backtracked and said she wasn't sure it was my brothers, it just came from his account 2) when asked for evidence, admitted she didn't have any 3)told my mother that the group chat never existed but 4) told me that the group chat existed, and she posted a dic pic to it, but It wasn't his?

AITA for wanting the whole story, or should I believe the girl??? I feel bad, because she seemed nice and didn't have a reason to lie??