As for spinsterhood being preferable to marriage to an irritating spouse .. I am prepared to accept that for Charlotte her pursuing and accepting of Mr Collins as her husband, is a clear and unequivocal preference for marriage (indeed marriage to anybody) over spinsterhood.

And the following words suggest she has thought about the marriages she is aware of and this is reference when she says the following to Lizzy "I am not romantic, you know; I never was. I ask only a comfortable home; and considering Mr. Collins's character, connexions, and situation in life, I am convinced that my chance of happiness with him is as fair as most people can boast on entering the marriage state."

And Jane herself agrees (independently) with Charlotte's approach when she suggests to Lizzy that: " [she] confessed herself a little surprised at the match; but she said less of her astonishment than of her earnest desire for their happiness; nor could Elizabeth persuade her to consider it as improbable." I believe the reference to it as a reference to Charlotte's happinest.