It was not only insensitive of your doctor but also rather irresponsible for him to take her straight off Codeine containing medication, doctors are always taught to -wean- people off medications like that because of withdrawls.. I know what the addiction is like because for a while there I took it recreationally and developed a nasty habit which almost put me in hospital. The tolerance to the drug builds -very- quickly, and so does physical and psychological addiction.
The withdrawl for me was an INSANE amount of itching, like a chasing itch.. you know the sort you scratch but its moved to another spot already? Cold sweats, headaches, loss of appetite, completely irritable. It's not a fun time at all, I feel really bad for your mother
What I suggest you do is go to another doctor and explain the situation and offer some old filled prescriptions as proof that she has been getting the codeine for pain-relief. If they still don't do anything for your mother, you could go to the pharmacy and pick up the lower-dosage Codapane Fortes or a generic version and help wean your mother off them yourself. I believe the highest dose of codeine per tablet they are allowed to sell OTC is 15mg, whereas your mother would have been on something like 30-60mg per tablet by now I assume?
I'd ask the chemist if there are any drug interactions between the Codeine and this new patch thing, just incase.
Sorry if this hasn't been helpful, or if I didn't really post in time. Thought I'd add my bit.