CraigWal,
The physician you are speaking about is a physiatrist. This is a physician who is a PM&R specialist (physical medicine and rehabilitation).
With pain, this close out from surgery, an infection must be ruled out. The patient may not exhibit overt systemic symptoms (fever, chills, malaise), but continued pain around a total joint is always worrisome.
Once infection has been ruled out, then the history and exam should guide the attending physician.
Pain at rest is different than pain only with activity. Start up pain tells the physician something else. Try to have your wife determine when the pain is the worst and what makes is worse and what makes it better.
Note any associated symptoms, such as electrical shock type of pain, burning pain, and numbness or tingling in the thigh, leg, or foot. These point to a neurological etiology, either with the peripheral nerves or the spine.
In some patients, the total hip replacement lengthens the limb some. This lengthening can sometimes put stress on the sciatic nerve, causing pain. It can also stretch the muscles, causing them to function a little differently.
Even though the hip doesn't hurt right now, it is known that hip problems can sometimes cause referred pain to the distal thigh and knee.
The MRI of the thigh should have ruled out any muscle tears or if there were any post-op hematomas within the thigh.
Though micromotion of the femoral stem causes pain in the thigh, it should not be severe enough to cause a patient to go to the ER. Bothersome, yes, but not excruciating.
As you can see, so many things can cause problems, and they can be located in other places other than the thigh. It is going to take some work to figure this out.
Good luck. Hope the physicians figure out what is going on and your wife feels better soon.