Collapsed Brake Pipe
 

Previously i moaned about the missus having a temperemental rear drivers side brake issue, her brakes would overheat on one side only to the extent that is would be smoking but only from time to time. I hear of there being an issue with brake pipe rubber flexi's collapsing internally that lets fluid in but not out causing brakes to stick on. I have only ever heard of it happen with front caliper flexi's doing this, not rear brake drum flexi's. Could this be the answer to the problem with her drivers rear brake drum. I have now tried everything and that one rear brake is still playing up and squeeling and over heating

Not guaranteed to be the problem. The pads could be stuck in the caliper, the piston could be seized or as you stated the flexi may be corroded inside causing a valve which won't let the fluid back out. I would suggest removing the brake caliper and pads, checking the piston and cleaning the slide area for the pad. If this doesn't cure it, change the flexi. They don't cost a fortune and are simple to change.