As a mother of two DDs in their twenties, I am surprised by how many people are advising op to leave well alone.
FWIW I hold exactly the opposite view.
Personally, unless you were abusive or an addict or cruel in some way to your offspring, I don’t think that as a mother, you should ever give up, especially in this case when it doesn’t sound as if op has done anything obviously wrong.
Obviously there is a huge back story which you have left out op but on the face of it this sounds like it could be a case of classic parental alienation perpetrated by your ex if you ask me! Your dd has only heard his side.
There is a massive difference in age, understanding, and maturity between twenty and twenty-nine years.
And this is an opportunity to write one letter or message to your eldest dd to congratulate her on her pregnancy, to send her your sincere love and best wishes for the future, to apologise sincerely for letting her down and not being there for her in the way she needed you to be, to say that you don’t wish to intrude in her life if she still feels the same way, but you would welcome an opportunity to apologise and talk to her face to face if she felt that might be possible?
And you can say all this, while making it very clear that you don’t want to use her younger sister as a go-between except this once, and from this point on you won’t intrude upon their relationship.
Say that if she doesn’t want further contact, although you will obviously be sad, you will understand and leave her alone, but make sure she understands that you are always available for her or the baby should she ever need you, and your only wish for her is her happiness with her family.
Leave the ball in her court op. One letter in a decade is hardly stepping on her toes. And most DDs need their mums when they have a baby.
For all of the daughters posting here saying they would be upset to hear from their estranged parent, after nine years, I am sure there are at least some who would say they would be equally upset if they didn’t hear anything from that during that amount of time.