This isnt so much of advice as it is what happens in our house. We have an older dog that Gunner(our OE/bull mastiff) follows around. If she poos he goes behind her, smells and usually a short time later does the same.
Maybe she needs smell stimulation to go and do her business.
Also, do you have a fenced in yard? Kira, our older pup, wouldnt poop on leash, she had to be free to do her business without prying eyes...lol and im not kidding. to this day if we are outside she will go on the side of the house where we cant see her!
Best of luck to you and your girlie. When you have a chance, we would love to see some pictures of her.