Alma was jealous of Walter's closeness to Mahler in areas of Mahler's life
where she wanted to be pre-eminent -- his music.  Walter was designated by
Mahler to finish up the preparatory work on Das Lied and the 9th, and I can
visualize Alma's intrusions on that process.  I remember Alma complaining
that, after a performance Walter gave of the 4th in New York in the 1940s,
that he didn't escort her home from the concert.

She must have been a total pain in the butt!

Well, she really was.  I knew Anna a bit, and she told me stories about her
mother.

So that Alma was not a reliable source.

Bill S