Thank you so much Pels for your excellent suggestions. I had reached a block in my thinking, and you have shown me a new door to open. I don't want to say too much in this first message, but it is important that I underline my sincere thanks to you.
As it happens, my Elizabeth Peach was married before the 1841 Census. She died before the 1851 Census. The only facts that I have is a "Y" in the 1841 Census for Ashby de la Zouch, Leicestershire, plus also the age on her Death Certificate which is the same as the age in the Parish Records, and finally the name of a witness at Elizabeth's wedding - Martha Handley Peach (who was Christened in Ashby de la Zouch).
I rule out the 1789 Elizabeth because my Elizabeth was born in 1786 or (slightly less likely) in 1787. My guess is that County boundaries were not a serious concern of the average person. So after 30 years of searching Leicestershire, including many days of reading page after page of Parish Records in the Leicestershire Records Office, I have turned to think about the neighbouring Counties. But of course this involves several hundreds of Parishes.
I will post a second message tomorrow which gives more information.