Gluesister should make the effort to reply to all of us Tidy, even if it's just something like "Thanks for getting back to me, I appreciate your reply" and she still wouldn't have to act on anything one way or the other.
She wouldn't have to talk to her sister or take one side or the other. Just acknowledge that she has received Tidy's reply.
It's only polite when you consider that she asked Tidy for her side, to then thank her for taking the time to send it when she really didn't have to.
No matter what Gluesister thinks of it now she has it, she should at least acknowledge she's received it.