If she comes from a country which requires a TRV (sticker in passport), then she should have the Visa in passport.
If her current TRV is still valid, she can re-enter with that plus carry the OWP as well.
If the TRV has expired, then new one needs to be applied.
Only exception is if she re-enter from USA via land border then she does not require TRV in passport.
(But to enter USA, a US Visa would be necessary).
If she is residing here and has OWP and a job for some time, no harm in applying a US Visitor Visa too.