Bringing her in the loop on plan 'Invite Kyoko and Yuma to the picnic for MAXIMUM FOODINGS/SOCIAL' sounds good to me, actually. We're running the idea by Mami soonish, right?
I don't know. We should prepare them both a little for the reconciliation before they actually meet again. Mami resents Kyoko for leaving her, and Kyoko doesn't know exactly how badly off Mami is doing and how big of a mistake leaving was. Combine that with Mami limpet and Kyouplomacy, and it could end very badly.