CALIFORNIA: Would you let your husband's new girlfriend throw a party for your five year old? Would you attend? Justine Musk did

Elon and Justine Musk are not divorced yet. But he’s living with another woman and she is dating while they hash out their divorce. Elon was in the news yesterday because of some project with SpaceX, one of his many successful companies. He had a successful launch of sorts and things are looking promising as far as aiding him in bringing space flights to the private sector. So it gives me an excuse to talk about their divorce situation, specifically this post I read on his soon to be ex wife’s blog that Elon’s current twenty-something girlfriend had thrown a birthday party for his five year old with Justine. And Justine attended! I personally thought that was incredibly mature. It is one thing to accept your ex has moved on, and quite another to sit as a guest as a party the new woman is throwing for your  child. Justine must be totally over Elon. I don’t see how there is any way she could stomach this scenario other than to say she’s over him and she is the one who wanted out of the marriage.
Why can’t more couples divorce like Elon and Justine? (Well, actually, maybe I’m speaking too fast. Elon and Justine are having their own share of divorce contentions and their case is in appeal as we reported in a previous blog. Something to do with the money allocations. But at least, they are doing well with the kids, right? BTW, they have four sons and they share custody of them.)