Anyone who uses this as the sole basis to decide if pay is equivalent between people has no idea what companies actually care about.
She sounds like a nightmare to manage.
She said she found out from a W-2 on the printer. I worked with a guy who found out a co-worker was making $10k more than him based on a paystub left on the printer. They were both guys and relatively new hires. One simply negotiated better coming into the job I suppose. I talked the guy making less off the ledge and he went to work. He was a better worker in every way vs the guy getting paid more, and over time it worked itself out. He ended up getting a bunch of promotions and raises, while the other guy eventually got let go. Working harder is the appropriate action, not filing a lawsuit. If she leaves Apple, who is going to hire her knowing that’s now her move?
The claim that they were hired at a lower pay that never got changed to match the same track as higher pay employees is also just an issue that affects everyone. It even has a name - salary inversion.