child has vile bad breath for years! Dr. & dentist no help

Has an apointment for my 8 year old at GP and not leaving untill they sort this issue out as iv been back and forth between diferent dentist and doctors for her for 4 years but the problem is still there x
now dentist have given her full clean bill of oral health teeth gums and tongue x
and she doesnt have tonsil issues infact very rarely ill ever she probaly only gets a cold once a year if that she hasnt vomited for about 2 years and that was caused from croupe not a stomach issue x
her toilet habbits are completly normal once or twice aday no pain not loose x
and her diet is remarkable for a child these days as i make the point of counting her fruit n veg aday and she has atleast 5 inc 3 bits of fruit with her lunch 1 with her breakfast and usually 3 veg with her dinner and always varied so plenty of greens x her calcium intakes sufficient milk on her cereal plus a glass before bed x
she brushes her teeth and tongue in the morning then uses mouthwash when home from school becasue of her lunch and then brushes again for atleast 5 minutes before bed x
BUT.... garenteed within 5 minutes of brushing her teeth even when i do it for her and using the fancy adult toothpastes there is no longer a minty fresh breath its actually vial as it smells like cows mannure... i know that seems mean and i do have to tell her not to breathe in my direction as its made me gag but even if shes 2-3 foot away it really really that bad, im worried about what other people must think as still 4 years on no matter what i do or where i take her i still have no answers!!!
serious answers please anyone thats gonna be nasty or sarcastic dont waste ur time this is a childs health im referring to and dont need no nasty comments want genuine advice as the doctors are a joke!!! x