They existed, we know as much. In the so-called Munby Letter (middle-earth.xenite.org/2011/12/08/what-is-the-munby-letter/), Tolkien states: 'There must have been orc-women. But in stories that seldom if ever see the Orcs except as soldiers of armies in the service of the evil lords we naturally would not learn much about their lives. Not much was known'.

Which means license to invent, right? Any place, any time, any orcish culture - or how about an orc woman re-embodied in Aman (if you go by the corrupted Elves theory anyway)?