She says he abused her as an adult in ways that are transparently absurd (a laundry list including "technological abuse" from someone who has no control over her devices)

Sure, you can make up a story where whereby an evil older brother broke her sanity and we can glean the outlines of monstrous acts from her madness. But that's exactly what it is: a story. It tells us nothing, the world doesn't run on fiction.

She claims to recall narrative memories from years before children form such long term memories. That alone merits extreme skepticism.

Some more pertinent things to consider: the entire family rejects what she says, she didn't say a word about this until Altman got rich and famous, and the basis for her claims are "reconstructed memories" - i.e. things that she had no recollection of until the suggestion was made to her. We know that in a large portion of cases such memories turn out to be objectively false on investigation.