You do not have a right to employment
My friend is not be specifically claiming that she's entitled to a job, but her complaint that she "deserved equal opportunity in work" is another way of phrasing the same erroneous argument. Both are based on the belief that there is a "right to employment," which is a mistaken assertion that you have the right to someone else's property. My friend was an "at will" employee, so her employment, as well as the quantity and level of work she is given, was purely at the pleasure of the company's owners and their agents. Was it "fair" or "right" that they fired her, instead of helping her advance in the company? My friend does not believe so, understandably, but the only judgment of "fair" that counts is that of the owners and those to whom they delegate managing authority. Your employer is in no way obligated to give you opportunities, no more than your neighbor is obligated to hire you to mow his lawn even though you'll do it cheaper and better.
Now let's consider my friend's situation from the company's perspective. The first person was a veteran, and I suspect that her expertise was needed on projects that couldn't have been given to my friend, who had not done this job before. The new person already had experience from a previous job, so it makes sense that he would be given better resources to perform the advanced work that a rookie cannot do. Still, it wouldn't matter even were they the most unqualified in the department: it is still the right of the company owners to be stupid with their own property -- provided they do not harm others. Declining to hire someone, or deciding not to continue someone's employment, is not causing harm: if it did cause actual harm, that would imply a right to the employer's property. On the contrary, forcing someone to hire another harms the employer, because it is forcing the owners to dispense with their private property against their wishes.
Of course, my friend is not (yet?) in a mindset to accept what I tried to explain, which does not mean I am unsympathetic. I personally know it's very hard on her that she's out of a job, especially at this time of the year. She has children, and suddenly being out of a job throws a wrench into her holiday plans, but companies after all are in business to make profits for their owners, not provide charity. Charity comes after companies have maximized profits, so that their owners and employees can afford to be charitable.
Hopefully she'll realize that the answer is not pursing a lawsuit, or standing outside their offices handing out leaflets, as she is threatening. She has no basis to sue, and more importantly, she will be wasting energies that she should put into finding a new job. She accused me of accepting a company walking over me, asking rhetorically whether a woman should just accept being raped. That's more than a stretch: that's an absurd comparison. Rape is a violation. Losing your job is merely one party deciding not to continue the commercial transaction.
Moreover, as I told my friend, if one company won't open doors for her, another one will. It's time for her to find a job with someone who wants her to succeed, someone who values what she has to offer, rather than waste her time at a company that grudgingly keeps her on. That's when everything will work out in the end. Her former employer, for whatever reason, has decided to deprive itself of her talents and abilities, and a better company can now make use of her.
How much do you "deserve" in pay?
If your compensation isn't enough, why do you work there?