Re: red flags everywhere or am I crazy?
Unless she offered to take it thinking that would somehow convince you she's innocent and you wouldn't make her take one, in which case she could be guilty and she does fear a polygraph, and the threat of the test might actually get a confession out of her.
I'm betting this is the case because she pushed him into therapy to convince him of her story and then got super nervous right before therapy. Someone who is telling the truth doesn't get nervous right before they have to talk about it with a neutral third party. She's probably doing the same thing by telling him what he wants to hear and then worrying about how she's going to pass when it actually happens or just convincing him it's wrong if she fails. She's tried to convince him and manipulate him over all sorts of things up until now so why would she suddenly do anything differently?