Jo would have been terribly distraught if she knew just how down Farren was feeling; on the other hand she would have appreciated knowing someone else felt the way she did. Not that she thought any of her siblings felt anything more than like absolute shit, of course. It would just have been nice to hear it out loud. But then, Jo had been guilty of staying strong in front of them too - barring that first few hours after she had gotten the news about the school.
When Farren took off Jo rolled to the upright position and looked around, following in her sister's tracks immediately. Oh no, she thought. Farren was going for Sam and yes, Jo knew what she meant - she meant well, she wanted to include him in the playfighting. But something told Jo Sam wasn't going to be into that. She ran faster, trying to get there before Farren and run interference. It could have been perceived as playing rather than a bid to protect the white wolf. Farren seemed to understand that you couldn't pull Sam right into it, however. She was tame in her interactions by her usual standards.
Just in case, however, once Farren swatted Sam with her paw Jo growled softly in warning at her, and then heabutted Sam, as if to tell him it was okay. They just wanted to have some fun, no one was going to hurt him.