If the smell is that evil but her digestive system is working normally I'd guess at a lip fold infection. The smell really is vile.
I know you've said the folds are a bit wet, but is there any staining there? I don't know what colour Isla is, but when William, who is a mainly white coloured orange roan, used to get lip fold infections, the folds would be stained brown.
I think you may have to do a close up sniff test! Or you could gently wipe the lip folds with a tissue then take a deep breath
Teething problems are another possibility, as others have said, but I don't think the breath is really evil unless there's a problem tooth. Will she let you look in her mouth?