Q:

Ancestry of Christian Penn (d. 1684; m. Francis Eaton, then Francis Billington, both of Mayflower)? 

Does anyone know the ancestry of Christian (or Christina) Penn, who came to Plymouth colony on the Ann in 1623?   She married first Francis Eaton (Mayflower) then Francis Billington (another Mayflower passenger).   
Several family trees try to tie her to the Penn family through the Admiral Sir William's uncle George, but that seems unlikely, and many of those trees have that uncle George dying in Plymouth in 1632- which isn't likely to be true as the Admiral Sir William's will in 1670 refers to his uncle, "George Penn late of the fforest of Brayden in the County of Wilts gent Deceased".   Which makes sense, as George was the eldest son and named his grandfather's main heir and executor in the grandfathers 1590/1 will, making him the owner of Penn's Lodge in the vicinity of Minety, Wilts.   This points to the likelihood that George Penn also died there and did not go to Plymouth Colony.   
I haven't been able to find any sources of Christian Penn's ancestry other than the ones that tie her to Admiral Sir William's extended family.   
While family trees up to the point of the Mayflower are well-established, I'm having trouble going further back for Christian Penn.   Does anyone know whether she is a cousin of THE Penns?   Or who her people were? 

A:

WeRelate lists Christian Penn as a daughter of George Penn and cites Shaw as a reference for birth, but since I don't have that reference myself, I cannot validate whether the birth reference is only the date or includes the parents.  
You might want to start a discussion on the 'talk' page for her at werelate.  No one had previously started a talk page there but there are 8 people 'watching' her so one of them may also be interested in assisting you.  I started a talk page and referenced this question.  
Besides potentially getting you an answer, it may get some other contributors to G&FH SE.