I need an earphone when in these sessions - that is an audible I could have made great use of!
When she says something that's just so incredible that you can't think of a response (and there are usually MULTIPLE instances of these), just say something like:
"Wow." (staring at her, shaking your head). "Unbelievable."
or
"Amazing. Really."
or, if you're feeling kinder,
"I'm sorry you feel that way. But I haven't changed my mind about anything."
or
"I really don't feel like discussing this right now."