Is it possible for a np to miss 4th or 5th metacarpal fract. she was looking for frac. below thumb. that's where the bruising was?

It is possible : It is possible for anyone even a trained radiologist to miss a fracture on Xray. If you are still having pain in a week from injury get examined again.

Yes: It is possible for anyone to miss a fracture on a X-ray. Doctors, PAs, NPs, and others may miss things on X-rays sometimes. X-ray doctors, called Radiologists, train for many years. Some of them do fellowships, engage in additional studies for a year, to become musculoskeletal radiologists. It happens. your concerns are understandable, though.