Is it possible that there's more going on?
My sibling is trans. We have been nothing but supportive, respectful, using preferred pronouns, name etc. which are all now legal - birth certificate and passport changed. But they have always been quite manipulative and spun a narrative to others that is simply just not true, to suit their agenda.
Last year, my husband, other sibling and I supported my trans sibling through a significant life change/event in every way - they were homeless, penniless and in poor health and we supported practically, financially and emotionally. In this situation, we later became privy to the other party's perspective, and saw hard evidence that just didn't tally with what my sibling was telling us (police reports, property damage etc.) As soon as they were challenged on this, without us withdrawing any support, everything changed. They upped and left, very quickly found a new partner and circle of friends, and told them all that my husband, other sibling and I were transphobic (we absolutely are not) and abusive (also not!) to them and thats why they dont have any contact with us any more. Truth is, they just didn't like being called out on their behaviour.
Creating a narrative in their own head isnt a new thing, they had an old online presence in the earlier days of Facebook where they referenced being an inpatient on a mental health ward and detailed their whole experience and created an entire persona around this, all of which was untrue.
I have long suspected my sibling is autistic, and there has always been a need to control situations as part of that. I also, having had them living here for 6 months, strongly suspect a personality disorder too. They are very selfish, and rarely think beyond their own needs. My sibling also seems to move from very quick, intense relationships to new, equally intense relationships with partners/friends without maintaining any connection with the previous groups. And now this seems to include family too.
In short, nothing we did or didn't do caused or could have changed this situation and the door is open for them to resume contact when they want to.
I can't imagine how much more difficult this must be to be losing your child. How may she respond to being asked outright as to whats wrong and why isnt she responding?