Congratulations on determining that Rachel's treatment was discriminatory.

This sort of bickering reminds me of an incident when I was at university, a certain member of my cohort, who was from down south was in the habit of coming to lectures and seminars wearing football shirts.
Another member of the same cohort who was local confronted him on the second week of the first semester.
"You came in here last week wearing a Hull City shirt," he pointed out.
"So what?" said the first guy genuinely surprised at the aggressive tone.
"This week you are wearing a Birmingham city shirt, that's SO WHAT!"
The rest of us by this time were paying attention, because the second guy sounded fit to burst.
"Oh," said the first. "I just like football shirts, they are comfy and I like all the different colours and patterns."
The second chap, went red in the face and gritted his teeth.
"You cannot do that!" he snarled.
"I can't do what?" Asked the guy in the shit as confused as the rest of us.
"YOU can't just wear a different football shirt every week just because you like the colour. Don't you understand, you DON'T do that, its not on, team loyalty IS IMPORTANT!"
The first guy was puffing and steaming from his ears, his face was red and his fist were clenching.
At this point the lecturer entered the room and asked what was going on and the first guy began literally screaming that the shirt guy had to be sent home to change or He was "going to KILL stupid southern ponce".
In the end Loud mouth Mc shoutyman was escorted out of the room by security.
However that is not the end of the story.
Our film studies lecturer told the story to to the head of the sociology department who far from agreeing he had done the right thing demanded Shirt guy be called in and ADMONISHED for being deliberately provocative and knowingly causing trouble by wearing varied football tops at a university in a town that was notoriously football mad.
The upshot was that Shirt guy left the university and sued for his fees to be returned and ultimately won, Shoutyman was hailed by the other local students as a hero.

I told this story to a close friend of mine who was a keen supporter of the local team and who was also a professor of English at Durham university.
His reaction astonished me, far from agreeing with me this this whole incident was raving mad, he got very angry and assured me that had he been the lecturer, he would have physically ripped the shirt off Shirtman's back, kicked him out of the class and told him to only come back if and when he made up his mind which team he was going to support or when he had decided to not wear Football tops at all.

This was the first time I realised that tribalism is alive and well and deadly in the modern age, and that some people can be brought to the verge of homicidal rage by actions of another that mean nothing to almost everyone else, simply because they buck an accepted local norm.

And your point is, nobody is allowed choices? Or....?

Are the accepting/rejecting bodies truly equivalent in these comparisons? Who, exactly, is doing the accepting or rejecting? Are they the same body? Do they even overlap? Are the specific human beings who accepted Susan the same specific individuals who rejected Rachel? And what relationship do these individuals have with the progressive ideology of "Social Justice Theory"? Is there an official membership status or list of individual names of people who self-avowedly belong to all three of these clubs, and are recognized as members by some authoritative official? Or are we just tossing an apple and orange salad?

Race is part of your essence? Isn’t this purely a societal construct? Perhaps that is why those of mixed race often feel they have no place. When my son applied to Washington University in Saint Louis, he felt pressured to join an organization of others of mixed race. He found it repugnant — this insistence on defining oneself by ones racial heritage, and thus he chose to go to a different university. Perhaps it’s our human nature to be tribal, but this shouldn’t be conflated with the false notion that race inherently defines who we are. The various races have the same genes, all aligned in similar positions along our chromosomes! And this makes us one species! Shouldn’t we try to overcome our tribal natures rather than to adhere to this tendency with this false ‘race-defines-your-essence’ nonsense?

Race is a false concept. But, the fact that people of color have been and continue to be discriminated against is a fact. The same can be said of people from ethnic backgrounds different from those we are accustomed to.

You list yourself as atheist. Your social justice and labeling issues is no different than you labeling yourself atheist. If you notice on link I provide below, people are recognized as gods. Gods exists because people labeling themselves as gods. If a girl can label herself as a boy or a white label themselves as a black then people can label themselves as a God and thus atheism is wrong or illogical.

Now that you are given the fact that gods exist, why are you still calling yourself atheist? Is this a refusal of acknowledgement that people are self labeling as gods? Are you labeling yourself as atheist for same as a "white" person wants to be called "black"?

[en.m.wikipedia.org]

I am a me. As my parents would say at dinner, like it or lump it. (I still don't know what that means.)

Your inconsistency only exists in certain communities, most notably yours. Although you only used it as example in this instance, the definition of race can of itself be part of the problem. Race is defined by externally observable characteristics in may places in the world, but in Aussie, race is defined as acceptance within the community or culture. That is, regardless of colour, if you are accepted within the indigenous community as aboriginal then that is what you are. So, anyone adopted into that community via marriage or any other means, is accepted as part of that race/culture. It's not necessarily the best or only solution, but's it's better than measuring "race" by percentage blood. In the indigenous institutions there are signs on the wall saying "don't judge my aboriginality by my colour".

To take it to its extreme level for the sake of argument. What about species ? What if I decide that I am a dog or a cat, rather than human ?

I suppose that the question really generalizes as. To what extent does an individual get to define themselves, and to what extent are we defined by society as a whole ?

The one obvious answer, is that a thing, or human, may be defined in several different ways for different purposes, by different people. As for example. For tax purposes a car may be defined as a road worthy vehicle, when I use it to drive, and taxed accordingly. But the tax authorities may define it as and exhibit, when it is in a motor museum, and decide not to tax it.

So it should be possible, that for example, a human may define themselves as Female, for the purposes of sexual relations, yet be defined as Male, by a sports association for taking part in sports. But that requires that people are able to be honest, even when self interest is a stake, and that people accept that life can be complex and that you can not always have simple hard and fixed definitions of everything. But that would require people to use their brains, and sadly they are usually very unwilling to do that.

Yes social justice theory is itself just a cultural construct, and your point is far from being the only fault to be found with it. Though it has to be said that "none existent" and "fluid" are not at all the same thing.