My daughter she is 7 years old and her mouth smells so badly even after brushing and using mouth wash regularly. What can I do....?

Add. Add flossing and tongue brushing to the routine and see if that helps. If her breath still smells bad speak to her pediatrician as bad breath could be associated with the digestive tract as well.
Check with dentist . If you have your daughter hold a mouth full of air then slowly let it out and smell the air and it is bad.. It is probably from her mouth. If she has stomach issues also may be from her stomach. Bad breath can also be a sign of a systemic problem.
Can be intestinal! Bad breath frequently is intestinal, not oral! i would try probiotics to help smooth out small intestinal bacteria. Chronic constipationcan also do this. If pro-biotics don't help, take her to your doctor! one other thing: a bad tooth can be the culprit as well.!