Parents who end up here usually didn't get a reason, or got one they can't make sense of, a short message or a conversation that referred to things they don't remember happening. The years after are mostly ordinary and long, birthdays where you don't know whether sending something is welcome, a grandchild you've met twice, and a lot of rehearsing what you'd say if the phone rang.
What tends to make it worse is treating the decision as a mistake she'll come out of, which is where the advice about being persuaded by the internet leads, since it turns her no into an error to correct instead of an answer to accept. Almost nothing gets reopened by a parent explaining why the account is wrong, and quite a lot of it gets reopened years later by a parent who stopped arguing about the account.
This is written for parents and there's another part of the site written for adult children, and neither one is arguing the other side is lying. The posts here cover contact that gets refused, what a first message might reasonably say, the relatives who take sides, and living with it when nothing changes.
Your sister sends you the article, the one explaining that estrangement is up because young people are on their phones learning words like narcissist and boundaries and toxic, and it's the first thing anyone has handed you in three years that doesn't seem to think you're the problem. That relief is the reason to be careful with it, because an explanation that puts the cause of this outside your house is going to feel better than any other explanation available, and feeling better is not the same as getting your daughter back.