Is she licking her butt a lot? Anal gland secretion can smell very fishy and I've often found if a dog with healthy mouth has fishy breath (and isn't eating fish) they might need their glands expressed and be licking at their butt to try and relieve the pressure.
If you catch her scooting her butt at all, that's pretty much a sure sign it's anal glands.
Yuck. LOL