Linda,
I am so sorry to hear what you and Carol are going through. I'm scheduled for surgery on the 28th and it is now my worst nightmare that they won't be able to do it. I can only imagine how devastating it must have been for the both of you.
I'm sure that when I had radiotherapy in 2008 and 2010 that I had Oxycontin in a liquid form for breakthrough pain. I was also on Morphine (in soluble powder form). I had no bad side effects (apart from constipation) and was in no way mentally impaired when using it. About the only thing was that my pupils were very dilated and I was sleepy at times, but the sleepiness was most likely a side effect of the radiation. I also had no problem in coming off it.
Don't be afraid of the Oxycontin, if she does have any unpalatable side effects she can always stop. As for recreational use, apart from getting rid of my pain, it did nothing for me so I don't know why anyone would bother.
Best Wishes to you and Carol
Sue G