Don't ask her anything. If she's hiding something, she's not going to tell you.
Verify independently.
Purchase and hide a voice activated digital recorder or two around the house or in her car where she is most likely to carry on a cell phone conversation when you aren't around.
You can return the recorders within 30 days (or more) at most stores if you discover nothing is going on.
Asking her resolves nothing because you'll still be suspicious and she'll be tipped off towards being more careful.
The internet is 90% complaining and entitlement and I hate it because I deserve better!
