Ah, one of the joys of living with dogs...
Has she by any chance rolled in fox poo? Or any other 'musky' animal poo?
(Fox poo is one of the most vile - and lingering - substances on earth. And one the dogs seem to prize above all other things.

)
If so, I've found that washing my dog in something tomato-based is pretty much the only thing that takes out this particular smell.
Tomato juice works well. If you have tomato paste, thin it with water to the consistency of a thick-ish juice.
Get your dog wet (with water), rub the tomato juice in thoroughly. Now comes the hard part - you need to keep your dog tomato juice-covered for a few minutes. Your dog will likely try to shake - which means you will have tomato all over the walls, floor and ceiling.

I wrap mine in a towel and give him/her a chew-stick or kong to keep him/her occupied.
After about 5 minutes, I then rinse my dog thoroughly, shampooing with regular dog shampoo if needed. You may need to rinse several times.
Is your dog white? If so, be prepared for a bit of a pink tinge. My collie sported a pink ruff for a few days...
If its 'only' normal non-musky poo that she has rolled in, try a thorough brushing getting as much dead hair out as possible. Look for dried poo bits still clinging to the coat - you'd be surprised how tenacious that stuff is! You can then try to shampoo again using a special deodorizing shampoo - this is the one I use:
http://www.drsfostersmith.com/produc...7&pcatid=18837
You want a deodorizing shampoo, not just a scented one. Scented shampoos tend to mask odors, not remove them, sometimes making an even worse combined scent.
You are right that most dogs should not be bathed frequently, but in an emergency (and I county gagging everytime you cuddle your dog an emergency

) you do whatcha gotta do.
My guys are breeds tending to dry skin, so they are not bathed regularly, only when they become over-ripe, about twice a year. Or whenever they roll in fox poo.
You could also try brushing baking soda through the dog's coat when dry. I've done this to get rid of 'oily-ish' odors in a bath-hating golden retriever (different kind of fur) when she got a bit too smelly. I've never tried it against a poo smell, though. But might be worth a try.
---
All else fails - I mow the grass, let the dogs play in the fresh mown clippings. Somehow, this seems to take out all odors - turns the dogs green, but they come in smelling lovely.
Good luck...