Hermione was used to explaining herself - just generally not while being accused by another girl of something catty. Generally, the only girls she spoke to were Ginny - sometimes Susan, and being accused of calling someone a name? Well, that had certainly hadn't ever been a problem that she'd had.
She had bigger things to worry about than insulting girls she barely knew.
She followed Lisa's pointing, though, and then rolled her eyes. "It's a wizarding mirror, Turpin. I don't know what it wanted you to see, but I certainly wasn't wasting my time coming up to you in hallways to insult you."