Who are "They" and what does the share price have to do with a new Chairman being appointed?
He’s being replaced as consideration for a settlement agreement with the SEC.
It seems likely Tesla chose Denholm because they have a bad PR problem, and it will be difficult for media companies to portray her as a villain.
Telstra is widely regarded as the worst company in Australia to deal with as a residential customer.
And she was the CFO so she isn't responsible for customer service.
Consumer-facing vilification in US media isn't really about what the person has done or what kind of person they are, it's more about what form of caricature can be depicted of them based on racial, gendered, and political stereotypes.
Denholm doesn't fit into a category of race, gender, and political affiliation that easily lends itself to a villainous caricature, and to the contrary does fit into such a category that would make it broadly unacceptable to consumers for a media company to create a villainous caricature of her. In other words, if a media company attempted to do so, it would damage the media company's consumer brand instead of Tesla's. This creates a disincentive protecting Tesla from attacks from media companies (all of which have a great financial interest in oil and legacy automakers, and very little financial interest in Tesla).
This is an increasingly common consideration for organizations responding to or seeking to preempt PR issues, especially for publicly traded companies with consumer brands, and other frequent targets of the media companies (such as police departments, private health insurance companies, and educational institutions).
But she is easy to cast as an ‘insider’, which is not what many thought ‘an independent Chairman’ meant. The cynics might suggest that Tesla chose her because she is less likely to rock the boat.