Travelling on H4 with H1B apprvoed petition

Can someone please advise for the below scenario: My wife was on H4 and her H1B petition got picked up in lottery and got approved subsequently. Following her H1B petition approval she left USA to get H1B stamping. Now the company which sponsored her H1B petition is not agreeing for H1B stamping as the project is not yet finalized. I understand that she can get H4 stamping done and enter on H4. My questions are: Suppose she enter USA on H4 and given that she has approved H1B petition (but no H1B stamp), can she look for H1B jobs? Can a employer file cap exempt H1B petition for her? Please share your experience if anyone has gone through similar circumstances? Thanks!