If it were me, I'd let the MC do the talking and just answer questions honestly (those about you, that is). Trying to "force" her into an answer or putting her on the spot will have a negative effect. I've been there. A good MC (good as in ones that actively work on saving marriages) will seek the answers you wish in their own way. Mine was excellent like that...however, my ex lied during our sessions so I'm not exactly sure.

Unfortunately, there isn't anything you can do. Just answer honestly. For your own self, not her.

There are moments in this life when you are so confident in the rightness of your actions, that not even for a second do you consider the option that you might be wrong.