She is quoted saying she no longer wishes "to be related to [her] biological father in any way, shape or form" [1]. Musk has publicly ranted about the estrangement, which isn't usually how one mends ties with family [2]. While I have no personal insight into the situation, it's fair to say Musk hates the estrangement and that his child, at the very least, wants nothing to do with him.
This is discussed in the Walter Isaacson biography that came out last year. Saying he “hates” his daughter is completely wrong and ignores first hand claims from both Musk and his biographer.
>Musk only learned she had transitioned through a secondhand source
>The wife of Elon's brother got a text, Isaacson wrote, which said: "Hey, I'm transgender, and my name is now Jenna". The text from the child, as in the biography, added: "Don't tell my dad."
>The biographer said that Musk was "generally sanguine" when he found out she had transitioned but was hurt when she cut off communication with him.
>The rift pained him more than anything in his life since the infant death of his firstborn child Nevada," Isaacson wrote of Musk's feelings about his relationship with his 19-year-old daughter.
>Isaacson said that Musk blamed the disconnect between him and his daughter on her schooling at Crossroads, a private school she attended in Los Angeles. Musk has made similar comments publicly.
>Last year, he told the Financial Times his daughter didn't want to be associated with him because of what he called the "full-on communism" taught in schools.
Usually when people say things like "this is the final straw" it indicates anger.
You can read more on the former by searching "Xavier Musk" and/or "Vivian Musk".