No training, no education, only good old heritage. I'm not even joking; it would be easier and even fun. The big sister you admire could teach you her profession, and you would learn from a teacher who knows you and land a position to test your knowledge instantly. It's a win-win: your sister gets promoted, and you enter the workforce with a brand new career path ahead.
Sadly, it doesn't work like that, at least for most modern professions, so everybody has to work their way in. This story, though, has nuance. I get that the idea of someone getting a job you fought for and studied for without training can make you mad, but if that person is your sister and she is struggling, why would you put your ego over her well-being?
The angry sister is getting promoted regardless, so she wouldn't lose anything if her sister gets her old job. If she can't learn the basic skills required for her new position, management would let her know, so what does she lose?
Obviously, you can't get someone inside a company so easily, but what's the harm in trying? Anything would be better than complaining online about your sister. Don't we talk anymore?
I'm surprised her energy is directed toward protecting her ego instead of helping her sister. Of course, I get that she might be acting a little entitled, or she might not know what she is getting into or how hard it is, but she will find out eventually.
Working with your siblings is complicated, and if she really wants to deny her sister the possibility, she could try helping her another way, right? Or at least she can explain that a tech job requires a lot of training.