YABU because if she thinks where she lives is a shithole, well you can laugh at her when she can't afford as good.
YABU to critise her wording 'unexpected' unless she was planned. You could reply, a wonderful unexpected surprise who turned into a teenager overnight!
YABU (depending on context) that she refers to you as a single mother on a low income. Again, partly she is a teen who probably thinks £20k per year is minimum wage, who will happy ignorantly state she'd never get out of bed for less than £60k (or wouldn't get in one).
YANBU to feel rattled by it. I was an utter knobber at 18, even though to the world I was rather 'with it' I just had an unrealistic outlook and that IS FINE, in some ways, you should be deluded as a teen as you should have fun, life will bite your arse so soon after that y'know, it's okay.
If your dd is anything like most teens, one day, when she's fully woman, scars and all she will thank you, she will understand, she will be extremely proud of you.
I only say this because I had a great young life, carefree, ignorant, blissfully fun, unappreciative. I only say this because I'm now late 30's and recently had a conversation (over wine) with my Mum and for the first time, truly understood.
I just thank goodness that there was no twitter or FB when I was 18. I am doubly glad that I wasn't linked to my mum. You're privvy to far TMI! I would have a chatt with your dd about her settings, I would step back from this knowledge, I would request that she's refrains from such blaze bullshit on twitter and restricts what you can see on FB.