You can't.

You just have to have eyes in the back of your head and watch her like a hawk.

I've not seen your other threads but if you think that Burns isn't suiting her then you could gradually change her to a different high quality dry food. You could try James Wellbeloved, I started my Golden Retriever pup on this but he could never get through the amount he was supposed to and I changed him to Burns and in comparison he got a lot less on that so it might satisfy her a bit more.
How is her weight? Is she about right? The best way to check it is to feel her ribs with the flat of your fingers. You should be able to feel her ribs easily with a thin layer of flesh between her ribs and your fingers. If she's a bit on the thin side you could try upping the Burns a little to see if it makes any difference before swapping her food.
Before I switched to BARF (Bones and Raw Food or Biological Appropriate Raw Food) my lot were on Burns and Sapphi, my Lab, was on High Oats as we had to watch her weight. She was never satisfied and was very food obsessed, particularly food we had. OK she's a Lab and they are food obsessed but this was much worse than she'd been in the past. Thats when I started to look into BARF, since swapping she's been much better, more satisfied and less obsessed and her weight is still under control.
I'm not suggesting that you should switch her to BARF, it takes a lot of researching, but if you feel you are still having a problem its an option once you've exhausted other avenues.
Having said all of that it is possible her scavenging isn't down to being hungry but just because she's a puppy. I'm looking after a 12 week old pup and I spend my entire time removing things from her mouth.... stones, twigs, hawthorn branch

, leaves, poo bags that she's knicked.....I could go on! All thats not because she's hungry its because she's a puppy.
Puppies are easily distracted so its inevitable that she'll be off to investigate things that catch her attention when outstide, have you got a "cue" that you say to ask her to wee/poo? I use "be clean" and I repeat it constantly to try and focus her mind to the job in hand.
Hope some of that helps!
