And now she knows she wasn’t crazy either. It’s really fked up to be openly gaslight by your SO. Not a cool feeling at all. You start losing trust in them and yourself.

I assumed she went along with it because he has been actively gaslighting her about how important this is to him. It’s just joking, he’s not serious comments while the frequency of them increases and the context of when and where they happen. So while she took him at his word he lied to her but she had a gut feeling it’s more than a joke. So she pretended to be ok just to see the real him. That’s my interpretation. Op can correct me if I am wrong.