When her poo's start ok and then go sloppy are you out on a walk?! Mine get like this on walks, I call them excitey poo's! The running around like mad things seems to make them loose! Paisley always squeezes about 3 poo's out during each walk and they get looser and looser, but the ones she does in the garden are perfectly formed!
Is there any mucus to the loose poo?! My great dane had diareha (can never spell that!) that was mucusy, he'd have it for a day, 24hours I'd starve him and then introduce scrambled egg and his normal food and he'd be fine for a while and then for no apparant reason he'd get diareha again, we got a fecal sample done at the vets (not cheap!) but it turned out to be campylobactor bacterial infection so he needed antibiotics to clear it up. Your situation doesn't sound as bad as that but if you can't figure out the cause it might be worth getting a sample tested to rule out some sort of gastro intestinal problem. My vet was also very keen to make sure he was up to date with wormings, so that could also be something to double check with your girly.