If you're not sure if you want to be trapped in a car discussing this for that long, perhaps "Let me think about it" is the best option.

Do you really think she's going to make a major proclamation in a car on the way to her mom's place?

But if you think you can have her along and that it might be beneficial and you can keep a PMA then why not?

M: 43 H: 39
D: 14
Married 15 Together 16
BD: 6/2014
S: 8/2014
OW revealed 10/2014
Instigated dissolution 12/2014, in progress
So over it!