"They walked me out like a criminal. They wouldn’t even let me get my bag.”
First off, since some people here may not be familiar with it, this is standard operating procedure at many companies, especially tech companies. there are too many risks in allowing someone back to their desk, people have destroyed or stolen information, caused scenes, excetera. Your items are delivered to you later. Acting as if this is some sort of aggression against her personally is either trying to get pity from those who not in the know, or simply a lack of experience of her own. I'm not saying it's a nice way to get fired, it's just common place policy at pretty much every place I've ever worked.
This reads like complete trainwreck of expectations.
1st mistake was taking additional work without properly legalizing it. She basically worked for free like a fool hoping that extra work will change into promotion. Hint: If they were interested in her leading team they would already set up her as team leader. Which means she never was considered as material for team leader but did enough work to stay in limbo of "well it works for now" so let it stay before we will find someone new.
Secondly personal relationship is the biggest factor in companies when it comes to promotion. There are some fields were proffesionalism is at 1st place but overall people want to work with people who the like. So if boss doesn't like you and likes new guy it means new guy will gets promotion not you. I have seen to many co-workers who would spend time assuming their work will naturally be appreciated and changed to promotion when they didn't realize no one liked to work with them really even if they could pull some nice numbers.
I'm gonna disagree with that. If you want a promotion I firmly believe showing why you deserve it is the best approach possible. Will it always work? No. But it screams "not a team player" to go to your boss, say here is something we need to do, and I am happy to help as long as you pay me more or promote me.
The way to get a promotion is to do your job well, be sociable, and have signs of leadership abilities [ie, respect of your peers]. That does not mean taking on other people's jobs. If you take on other people's jobs and become the Workhorse of the team, you do not get promoted. you're doing too much, and no new hire can easily replace you. Why promote the person that takes on all the extra work? That just hurts the team. Far better to promote someone that just excels at what they're supposed to do and has management potential.
taking on management responsibilities during a power vacuum without being asked is not a good move. If no one has mentioned to you that you're going to get that job, you're not going to get that job. Dontero has it right, nobody will stop you because it works for now, but those expectations were never going to be rewarded. In fact, stepping up into a management role during a vacuum often creates resentment. Depending on the situation, you can sometimes ask if you can take on certain responsibilities but being forward about your goals in doing so essential. If you laid out that you're doing this with the expectation of being in the running for the position, and were told to prove yourself, that's one thing... but silently expecting a promotion is a sure-fire way to never get promoted.
Sexism in the workplace definitely exists, but it's darn near impossible to get a sense of the truth of the situation from disgruntled ex employees and coworkers who may be friends of theirs. My wife for example, is underpaid. But it's also not in her wheelhouse to fight tooth and nail for a raise or promotion.