@SqidgeBum
"I know my baby is important to me and not other people, but I guess I saw it as her sort of brushing us to one side. We have had problems with her saying things about DD1 such as DHs nephew is her favourite and she wants to swap DD for other babies as they are 'less moany'. I have had to try very hard to include her in DDs life."
You know what? I was all prepared to say that you were over-reacting from your first post but then you dropped this in.
Under these circs I would now say YANBU.
What is the dynamic between your DH and his sibling in the family? Is the nephew his sister's or brother's child? And do you feel that their parents treat them unfairly - is one the "golden child"? (obviously not your DH)
If the other grandchild is to your DH's sister, then that's one tick for him being favourite (daughter's children often closer than son's children - not right but happens a lot)
If there is an unfairness between your DH and his sibling, regardless of whether it's a brother or sister, then that's a tick too, if the sibling is the "golden child".
If either of the above things (or both!) are the case then YAdefNBU, and your MIL is being horrible deliberately, and showing you that you, your DH and your DC are considerably less important to her than her other child's offspring.
Of course she might have just forgotten the sex of your DC2 - but it seems unlikely. It's a tiny, needle-dig to show you your position in her "favour" (not high).
And, as your DC2 is also a girl, it might be that she favours her grandSON. Maybe if you were having a boy this time, she might have been more interested.
Now a bunch of people might tell me that IABU for all these negative connotations I've put on your MIL's behaviour, but there are plenty of women out there who DO behave like this. SO many! We see the stories of them on AIBU, the relationships boards, "they took me to Stately Homes" threads etc. - so many parents who play favourites and set up these unhealthy dynamics.
I wouldn't bother making a fuss about your MIL's behaviour - if she can't help it, then a fuss won't achieve anything other than upsetting her, but if she's doing it deliberately then a fuss will a) delight her, knowing that she's got to you and b) create a massive storm which will upset everyone else too.
So let it go. But don't brush it off - wait and see what she's like when your DD2 is born, and then decide whether you want to expose your DDs to this sort of favouritism.