M-power doesn't have enzymes in it!! m-power would do bugger all with black top.
But yes hot Enz-all or hot power burst boosted with a citrus concentrate as the pre-spray.
A rug doctor? erm, to put it kindly NO, defiantly not! You'll struggle to get a half decent result on a lightly soiled residential carpet, never mind a heavily stained pub carpet!
There's no hire machine that will give you a good result.
I'd recommend leaving it alone and live with the dirt. Or get a pro in. The carpet could be a axminster or belgian wilton and will shrink on her then she'll be screwed. Best case scenario using a hire machine would create an even worse looking carpet that'll smell for weeks on end.
Get a few quotes in. She might be surprised with the costs. Might find a carpet cleaner that's willing to work for beer