Fentanyl and oxycontin together?

My wife is a cancer patient. She has been on large doses of oxycontin in the hundreds of mgs per day. It doesn't work any more so her doctor gave her 25 mcg/h Fentanyl patches. The patch has been on for 18 hours and it is not working -- she is suffering in pain. Is it safe for her to take oxycontin with the patch on? She has a call out to the doctor and he is not returning it.