I think it's definitely fair to say that we women are our own worst enemies at times and judge each other at least as much as men judge us, probably more so.
And you're absolutely right that other women will judge us for the choices we make regarding marriage, whether that is getting married too young, getting married too old, having children before getting married, not getting married at all, taking our husbands' surnames, not taking our husbands' surnames, calling ourselves Mrs, calling ourselves Ms, leaving the bastard, not leaving the bastard, changing our names or not changing our names back when we leave the bastard. The same way SAHMs and mothers who work outside the home are often bitterly judgmental of each other.
I do think a huge part of it is women wanting the way they personally live their lives - whether by accident or by choice - to be perceived as being the best way to live. Nobody wants to be pitied.
When I was on the train that day and I overheard a much loved teacher with a career spanning 30 years being reduced to an object of pity because she "deserved to be a Mrs, not a Miss", I realised that society absolutely will judge women based on our perceived marital status, whether we like it or not.
And women know this.@KievsOutTheOven knows this, because she is trying to control how she is judged based on her marital status. She doesn't want to call herself Mrs because she's not married, she doesn't want to call herself Ms for other reasons, so she calls herself Miss but publicly displays trappings of her long term monogamous lifestyle such as an engagement ring and evidence of her male partner and children. She wants to be a Miss, but only the young and cool kind of Miss, or failing that the feminist kind who rejects the institution of marriage, not the sad spinster kind.
You're right that we can't tell women what titles to use. At my secondary school, it was decided - at some point in the 1980s, I believe - that male teachers would be "Sir" and female teachers would be "Madam", because using "Miss" to refer to female teachers is a throwback from the time when only unmarried women were teachers because women were expected to give up work and keep house for their husbands upon marriage. We still knew whether someone was Miss Brown or Mrs Smith, but we called them all "Madam". The school did what it could, without dictating what titles women used to refer to themselves.
Personally I think the reason women still cling to these titles is because being married is a status symbol. When you're young, or at least not yet too middle aged to keep kidding yourself that you're young, you can be Miss in a young and cool way. But past a certain age, being Mrs confers greater social status.
It's spelled out explicitly in Pride and Prejudice, when the newly married Lydia Wickham, saved from perpetual shame by the skin of her teeth only thanks to the machinations of Mr Darcy, points out that she, as Mrs Wickham, now outranks her eldest sister, Miss Bennett. It's spelled out even more explicitly in Emma, with the constant references to "poor Miss Bates". And God forbid you ever become a Miss Havisham! We read and watch these stories and think it's a good thing society has move on since then. And it has, in the sense that you aren't doomed to a life of poverty if you can't find a man to marry you before your father dies and his estate is entailed to some distant male cousin. But I think the social cachet that comes with being a married woman still remains, which is why women still cling to these titles and why some women will even update their Facebook profiles to say "Sarah Husbandsname" in the middle of their own wedding receptions.
Unfortunately, whilst most women continue to cling to these titles and the status they believe they confer, our marital status and personal lives will continue to be considered public property, for any nosy randomer to speculate about to their heart's content.
Whilst men, of course, get to live free from all this crap.
It's almost worth doing a PhD at this point just to become Dr.