As stated in the article, he called her extremely biased against Tesla:
https://twitter.com/elonmusk/status/1450653942938054656?s=20Out of context, the tweet is largely innocuous as plenty of people might tweet such things. However, immediately following that tweet Missy Cummings was harassed ferociously by the Tesla shareholder base as seen here [1].
One of the leaders of the petition immediately following the tweet was Omar Qazi of WholeMarsBlog who is such a rabid fan and shareholder that he sees no issue with endangering children to support Tesla’s stock price as seen here [2] and the corresponding article. He also advocates for harassing any critics with vicious, baseless accusations [3].
Even if we assume that Elon is not directly organizing the attacks or by proxy, he has deliberately shaped a shareholding fanbase who will at the slightest mention. And, even if we assume that such a virulent base was purely accidental, which it never is, public figures have a moral duty to consider the likely consequences of their actions or speech.
His followers, many of which he engages with and responds to on Twitter such as the aforementioned Onar Qazi, are well known to viciously attack people he identifies as critics. These are not fringe elements, but the core of his fanbase. His actions are all but guaranteed to result in harassment of his critics, which is to his benefit, and he makes no effort to stop such interpretation, but rather harnesses it to suppress his opponents.
[1] https://twitter.com/MoodyHikmet/status/1451332679597625344
[2] https://twitter.com/WholeMarsBlog/status/1558122848601812993
[3] https://dawnproject.com/what-is-the-credibility-and-characte...