This is so, so silly, and I'm ready to get flamed, but I'm hoping posting on MN will get it out of my system.
I have a preteen DC from a previous relationship, and DH and I have a baby DC together. DH has raised DC1 from toddler hood. My ex is not and never has been in the picture. DH loves eldest DC, he is very much Daddy. By and large we are a happy family and baby DC has only added to this. I have no concerns regarding DH's treatment of either of my children, he is a kind and good man.
A few days after having the baby, SIL made a comment to me. She said "it's just so lovely to see DH Name with Baby. As I was saying to him, of course it's completely different when you have your own"
At the time I was exhausted, didn't know what to say, and replied along the lines of "newborns are certainly a shock to the system"
Afterward I felt angry. It felt like a hurtful thing to say, deliberately undermining the relationship between DH and DC, and I felt she was intentionally trying to make me feel insecure about how DH would be now baby was here.
It still annoys me at times that I didn't get to tell her how inappropriate a comment it was. Obviously I don't think about it all the