Difficult to stop her I'm afraid!! It's a charming habit lots of dogs have.
I can sometimes stop my dog, he does a thing where he'll sniff the poo, then have a little tiny taste, then he kind of moves alongside and if I tell him not to do it by that stage, sometimes he doesn't.
You can get a dry shampoo that you spray on and brush out which gets rid of some of the smell. I keep some in my car for emergencies when he smells too bad to be in there with him.
No its not difficult to stop. You need to get the 'leave it' on a reliable cue. Meaning you need to train until she does it every time, even from a distance.
Dogs roll in poo and dead things because the stronger you smell, the higher up in the pack you are. They do it round the neck area because when dogs are squaring up, the heads go over the necks of the other dog. The neck is a very vulnerable area on a dog
While you train the leave command try this - Carry a few fragranced baby wipes along with your 'poop-scoop' bags. They're great for emergency poop clean up - especially if you are out 'walking' in the car!