Hi Sam. Just a thought, but if Maggie's big teeth have JUST come in, the pong could be connected to this. Pickle's breath was rancid while he was teething, and not just when the little ones fell out, it stayed smelly until his adult teeth were fully through. It was a horrid smell, like rotting blood. He's not quite 6 months yet, but his breath has definitely improved in the last week or so.
Hope wee Maggie smells better soon - she'll be missing giving you kisses!!
Emma and Pickle xx