But do you really think Shouko just completely ignored Mana running off and didn't care one damn bit about it? Not only is that unlikely for what we've seen of her character, it's unlikely for any character that hasn't been explicitly made out to be disliked would do that. Maybe she hasn't been committing as much to her new friendship as Mana has, but that's completely understandable in that Mana is attracted to Shouko while Shouko is currently pursuing another woman; she shouldn't be expected to focus as much on their relationship as the person who's pining after her.
Well, that's my main problem with this manga, it's not exactly very well told
One would assume that it's normal for a friend to worry about eachother when they're having problems, but we're simply not shown that
Maybe there could appear another chapter focused on Shouko's point of view and maybe it could show that she was worried all along, maybe even bringing out the subject to the director, but the facts we are given at the moment is that Shouko doesn't show not even a single reaction to what's going on with her friend that they clicked so well at the beginning
Also i like this author's other works a lot, especially Lonely Wolf, Lonely Sheep, so i'm pretty confident that, if she wanted to show that their friendship is more than that, she could, in the end this is a story solely about Mana, with Shouko being nothing more than a plot device