I can see both sides here, to some extent, although it's a pity Mum and daughter can't communicate better.
I don't really talk about this much, but thought I'd give a view.
20 years ago, my DD and SIL had three lovely young lads. They both wanted a girl, so went in for a 4th child. The scan showed it was a girl, so celebrations all round.
At 25 weeks, at a scan, the hospital knew something was wrong, and said my DD needed a C-Section to deliver the baby, that night.
DD and SIL asked me to go to the hospital, which I did. In the middle of the night, my DD delivered my first granddaughter. Unhappily, a lot was wrong, and my granddaughter died the following day.
What followed was horrendous, especially for my DD and SIL, the aftermath and seeing that little white coffin, at the church, and then burying her, still rips through all of us.
During the next few months, I'm sure I got a lot wrong. In fact, I know I did. I just did my best, but everyone was fraught, it's not easy, and I'm sure I could have done better. My daughter and SIL were in bits, my parents were in bits, and it was just all stress.
Nine months later, my DD told me she was pregnant again. My heart sank, but I congratulated her and on we went. DD, SIL, and I lived that pregnancy day by day. The stress and worry were just awful.
My next granddaughter was delivered a bit early, but happily, she's now a lovely, happy, healthy 18 year old.
But, the point is that all parents get it wrong sometimes, as do all ACs. Unless there is abuse, a little more understanding, from both sides, might be better.
The pain of a child bereavement is just the worse, but it can be overcome with love and support.
For what it's worth, I have a policy of not passing on info that may cause trouble, so I'm unclear about the motives of FIL. But, I guess only he knows. I don't know why the daughter couldn't have sent a quick text saying all ok, but I suppose only she knows that.
I hope OP and her daughter sort it out. And, of course, I hope that this pregnancy ends up with a happy ending.