My guess, from reading Elizabeth Mavor's excellent biography, is that Eleanor was a lesbian, whether she realised it or not (likely not, as it was unheard-of until an outbreak of "sapphism" at the French court brought it to English society's notice in 1789); but that Sarah - if she had not met Eleanor at the impressionable age of 13, and if she had not needed to escape from her guardian - might have settled down just as happily with a husband.