^ Meant Methods of Administration
She implies has a habit/chronic use of oxycodone,or something that isn't Morphine. You can snort oxy, and, although rectal isn't what people think(it generally delays the onset of Oxycodone, longer Tmax and such, yet provides a longer duration; studies back this up) however it has a higher BA%. Do not remember offhand yet am pretty sure it is around the same as oral.
And Morphine is more potent with chronic oral use; high doses can also increase BA%. It is the same with oral diamorphine, which can reach 50-70% with chronic use of higher doses.
Just covering the bases, though you are right about surgery, true pain makes opioids more like the strong analgesics they are. Although, in deep wd, a GOOD DOSE of morphine should have someone feeling great, as with most opioids. Though it may have just been enough to alleviate wd, as dosage is unknown, although 8 mscontin 15mg wouldn't be that strong compared to a decent oxyhabit.
Oxycodone does effect the Kappa receptor as am sure you know, however don't think this is the reason for it's popularity.
According to literature, chronic oral morphine is about twice as potent, though don't have enough experience with it to say; oral Morphine simply didn't cut it.
Was just dissecting the issue, as Morphine was/is far superiority Oxycodone in my opinion, though again, you're explanation in this case makes sense