Is there a reason not to tell her where you are going? You can still be fairly vague, like "running some errands, then to work out."
What has worked for me is when she asks again, I just repeat what I've just said. She gets the hint, but in your situation, you may need to be overly transparent if you want her to continue to be transparent as well.
M:23 T:26 Me:53, Wife: 60 S:18 D:16 filed 7/16 W moved out 4/28/17