My response to her would be.

"I think we'll have to getting a sitter because I have plans too"

or

"I would, but I have plans too. Lets look into getting a sitter for the boys"

Me: 39 W: 33
M: 9 years
T: 10 years
S7 S10
BD 10/19/13
W Filed 11/25/13
EA Confirmed 2/2/14 (no evidence of PA)
WAW moved out 3/15/14