Jo caught a little bit more hostility in Molly's tone than she would have expected. While she hadn't exactly been happy with Dean keeping that secret, even she wasn't quite that angry.
"I'm all for sisterhood solidarity, but it sounds like there's a little more going on than just being pissed that Dean kept a secret from me. What'd he do?" Jo asked.
She knew that Dean was only beginning to trust Harry and that he was still wary of Molly. A lifetime's worth of seeing magic being handled in ways that were inherently evil made it hard to change one's mind. She understood it, but she still wished that Dean would give Molly a little more of a chance.