It seems to me, that any decent Law firm would have told her not to tweet about it imho. /ianal
It's your job to decide how much risk you are willing to take to speak out. Some fights are worth fighting.
Do you mean that is caught doing a lot of nasty stuff? The company has problems, it pushes against workers rights, it leaves towns that don't bow to their business tactics, it is sexist, etc. The "bad PR" is the symptom not the problem. Their actions are the problem.
However, in this case, it is already largely public and making Uber look the villain is a viable strategy given that Uber likely is the villain.