GMAT Sentence Correction (SC) | Isotopes in the recently excavated bones of a 14-year-old

Hi all,
I am well aware that there is something wrong with this question about the lack of "that".However,I would like to clarify some points,given that the missing " that" overlooked :
she had eaten a high-protein diet,so was probably the daughter of a gentleman,not a maid servant.
1)Using FANBOYS,can we assume "she" is ellipsis?--sha had eaten a....,so (she) was...
2)Which one is correct maidservant or maidservant's
To my ear maidservant sounds better.Is there any