That’s a tough one. Sunflower has only had it happen a few times that I’ve been aware of. It is even harder to catch as she also has occasional short term amnesia (and Meg has verified that Sunflower was “driving” when this happened).
One of them tried to impersonate Sunflower and did a pretty darn good job of it except for a few quirks here and there. I wasn’t even sure who it was for a while, but questioned them and they offered to answer any question that "only my wife would know" to prove it. I realized quickly, that was a rigged game.

Eventually I asked to talk to Meg. When she came out she explained how she was blocked and what happened that was backed up by other evidence. She also may have lied to her T and when called on it just winked. I think it was a kind of protection method.
What to do? I don’t have "the" answer. I’ve talked to them and told them it is okay to be themselves. Told them I accept them as they are and that it is safe and they won’t get in trouble. We aren’t on good terms yet, but we are at least occasionally speaking and I haven’t seen the impersonation since.