There is a link in Karen's link that is outdated but I found the right link to it: http://www.uwsp.edu/psych/dog/lib-prob.htm#copr

I read thru the suggestions a bit and it seems the best cure is prevention - seek and remove every pile of poop from the yard before she gets to it.

Since she is new and from a rescue perhaps it is due to anxiety and stress. Does she show other signs of anxiety like chewing on things and acting very submissive? Perhaps just training her in general will make her feel more comfortable with her position in her new home and over time she won't eat her poop. In the meantime just try to keep one step ahead of her in the yard .