I'll sum up the discussion that Ugolino and I had on Rolz about this issue. Essentially, what we are doing right now is pushing the Mami issue to a later date. Either way this interrogation plays out, the fact that we time stopped without Mami is going to be a major issue in our future interactions, but there are too many issues that we can't discuss in the presence of Mami, and the potential for a Mami freakout, or for Oriko to trigger a Mami freakout, is just too high to risk.
The plan right now is to downplay the "interrogation" aspect of our Timestop and basically go "We healed her and she surrendered, so now we are keeping her under close watch." It won't completely prevent Mami from getting suspicious, but it will (hopefully) take some time before Mami manages to piece together what's going on. During the period between now and when she figures it out, we hope to work on her loneliness issue enough to prevent a complete freak out. It's not a perfect plan, and it has several points of failure, but it is better than having to dance around her during the negotiations and there is less of a chance that Oriko escapes this way.
However the Oriko situation concludes, when we conclude the interrogation and exit the time bubble, we are going to be heading directly into another tricky situation with Mami. We still don't have an adequate explanation for why we didn't bring Mami in to help with the healing, or at least one that doesn't rely on Meta knowledge, so we'll need one before the interrogation is done.
Alternatively, if Mami doesn't believe us and presses and things start to go badly, admit that we had to threaten Oriko into stopping her actions. Which we most likely will have to do regardless, so it is at least a half truth.
Regardless of how we slice it, we are essentially setting up a time bomb to be set off at a later date with this course of action. Our hope is that we can buy enough time before the bomb goes off and remove as much gunpowder as we can so that went the bomb does go off, it doesn't do nearly as much damage as it would if it went off now.
Unless any of you guys have any better plans.