The Carano case isn't a free speech issue. It's whether or not they treated her with the same standards on her free speech as they do all other Disney employees. Since they say she was let go due to her Nazi metaphor then all you have do is look and see if they are firing or refuse to rehire other Disney employees using Nazi metaphors when talking about politics.
I believe she was not fired. They just didn't renew her contract or sign her to another one. Thus the idea that you can sue to get your job back doesn't make sense if you were no longer even a employee. At best she can maybe get some money for some kind of political discrimination by pointing out all the other Disney employess who have made Nazi comparisons online, yet stay employed.
That to me seems to be where the whole case is. Was she treated equally with other Disney employees when talking about politics.
Not renewing a contract and being fired is the same, just a different word, i.e. semantics. The effect is the same and it's just a convenient way for an employer to get rid of someone and be able to condescendingly say we didn't fire you ( we just don't want you around us anymore).
As to if she has been treated equally in the strictest sense i believe not but one has to also consider the various public levels. If an office worker with 100 X followers drops some Nazi comparison no one will notice but if his boss learns of it they might still lose their job, this happens on a daily basis with companies all over the world as people take carelessly to social media forgetting that it is read by everybody and in some cases might harm the reputation of the company they work for, which is grounds for dismissal.
Carano was a high profile employee involved in flagship projects with a high enough social media presence that put her on immediate notice to every news outlet that covers this genre and it may even spill into regular news. After the first time i think they have told her to knock it off behind closed doors, she didn't listen and inflamed the situation so she was "let go", i.e. fired. Actions meet consequences, plain and simple.
She has no one but herself to blame. When she signed the Disney contract she knew what Disney is about and what they expect. Behind closed doors executives might think the same but the public image has to remain squeaky clean and follow the current social trend to maximize profit, she got into the way with that.