Thanks all for your inputs. In the end, I had to email her about a few issues (S18's birthday, home equity payoff, etc), and included the child support issue as well. The email wasn't accusatory or inflamatory in any way, so it should work out all right.
M:23 T:26 Me:53, Wife: 60 S:18 D:16 filed 7/16 W moved out 4/28/17