I've just about had it with my DM. I've posted about my frustration with her before and how difficult she can be.
Her husband of 23 years has a 25 year old DD. He's never met her, knew she was born (as the result of a fling) and chose not to be a part of her life. He was with my mum at this point, I'd have been about 5 and knew nothing about it until I found a Father's Day card and letter when I was 18 (his DD sent them but he never responded).
When I found the card, over 12 years ago, I confronted my mum. She said that they never believed she was SD's DD, which the mum (we'll call her Carol) later proved. When my stepbrother visited his maternal grandparents, Carol would take her DD do she could get to know her half-brother (my step brother and her now have a close relationship). I think this is fine and actually very sad, but it rubbed DM and SD up the wrong way at the time.
To be clear he paid full maintenance until she was 18.
I asked my mum at the time how she could be with someone who ran out on his DD and her defence was "Carol should never have had that child, what kind of person keeps a baby from a fling" 
So yesterday I was FaceTiming DM (she lives abroad) and she was having a moan about SD. She said "he's in touch with his DD again". I said "again? I didn't think he'd ever spoken to her ever" and DM told me about 6 years ago he got in touch but it fizzled out. She said, in a very sneery voice "he got in touch as she'd had her second child, at the age of 19, with a different father than the first child". I asked what was wrong with that, and she replied "well who does that before they're even 20, she's turning out just like her mother" hmm]
To which I had a big rant about how DM is so snobby and horrid and judgemental and maybe of her wonderful husband had stuck around, and she'd had a father figure in her life, she wouldn't be a teen mum of 2. DM said I have to understand she's from a different generation to me - to which I pointed out that yes, in her generation having a child before you were 20 was perfectly normal.
I asked her why she was annoyed he's in touch with his DD and she said it's because he ends phone calls with "bye sweetheart, love you". She said she asked him what he was saying that for. I told her it's nothing to do with her. Apparently though when the DD was tiny she got harassed by Carol and her mum (what that has to do with anything now I'll never know). I said that if my DD had a baby by a halfwit who didn't wanna know if have something to say about it too.
So, the conversation ended on a bad note, but AIBU in thinking what I said was justified? Mum swears blind she didn't interfere when the DD was born, but TBH I know her and I don't believe her. She sticks her beak in when it's not wanted. She once had a lodger for a month who had a 3yo DD. The lodger owed her a bit of money when she left (about £50) so mum emailed her about it and included about 3 paragraphs about what a terrible mother she is because she'd shout at her DD now and again. Which is hypocritical seeing as I grew up in the Household of Screaming Slanging Matches.
I just can't believe someone could be so cruel and think that they have a right to say that other people should have had an abortion!