I'm sure your researchis impeccable Dot, but I had a similar experience looking for my Mother-in-law's ancestry. I struggled my way back to c1800 and then came across a "ready-made" family tree bach to c1500 and purportedly earlier. My first instinct was to shout hooray, my second to want to check it all myself! So no, I don't think you'll have spoiled her enjoyment at all. After all, Wainwright wrote all those books on the Lake District - hasn't stopped people climbing them, has it.
We had a similar "long-lost relative" story in my family. I contacted someone in Oregon who shared a ggg-gradfather with me, and who put me in touch with someone who was researching a bit further down the tree. She turned out to be in Australia and wasn't a blood relative at all but was "helping out" a relation of her partner. The helpee turned out to be my father's full cousin who lives in Nottingham! The family was split up in around 1918 and none of them knew anything about where the rest were.