Who is Lib Hancock from Year of Wonders and what is their importance?

Lib Hancock is Anna's best childhood friend and was married to a farmer before he died from the plague. Lib is the keeper of Anna’s secrets. Like the fact that Anys Gowdie had sex with George Viccars.. Lib uses this information against Anys when the angry mob accuses her of being a witch. Anna tries to reconcile with Lib but she dies of the plague before any amends are made.