Being forced to train my own replacement pre-layoff

TL;DR: I highly suspect that I’m about to get laid off, am being forced to train my replacement, am currently the only person capable of doing my job, and want to hold this knowledge for ransom.

Advice:

I (40F) work in the small (four-person) marketing department of a mid-sized company. Recently, my boss announced that we were bringing in a new hire, and from the moment this person started, it was apparent that she must have been brought in with the intent to replace me (…why? Because the person who originally hired me recently left my company… and my boss’s boss had never liked that person, and now wants anyone who was ever affiliated with her gone, as far as I can tell. He also hand-selected this new person, as they had worked together at a different company, years prior, which is never a good sign).

Meanwhile, I’ve worked at this company for 7 years, have never received anything less than a glowing review, and have often put in uncompensated overtime. We’re currently up against an insanely tight deadline to submit our annual catalog to the printers, and on top of all of the work that needs to be done on my end to meet this deadline (we’re talking 60-hour weeks for the next two weeks at a minimum, just to meet the catalog requirements), I’m now also being asked to show this new person all the in’s and out’s of my job… and it is quickly becoming apparent that she has NO idea what she’s doing, despite having come in with supposedly flawless credentials (and the holier-than-thou attitude to go with it). It’s not just the way we do things at my company specifically that she needs to be taught — she’s lacking some pretty shockingly basic industry skills and knowledge, which I have had to teach her… and she has already shown that she is the type to ask me how to do things privately, then turn around and act like she knew it all along (or came up with it herself) in front of our superiors.

In the time since she’s started, I’ve already done all I can to prove my worth to our shared boss, but to no avail – it seems like some decisions have already been made before I was even aware anything was happening, and it seems like it’s probably too late for me to change anybody’s mind at this juncture. I do know, however, that if I were to quit RIGHT NOW they would be absolutely unable to meet this upcoming catalog deadline without me (or to do a lot of other stuff, since I am the only one who currently knows how to do it at all)… and I want to use this as a bargaining tool, since I really feel like I have nothing left to lose at this point, assuming they’re planning to get rid of me shortly after the catalog deadline / finishing training the new person anyway.

My current, extremely rough plan is to contact my boss’s boss, tell him that I don’t have the time, bandwidth, or desire to train people who are ostensibly above my paygrade (as this person somehow is ?) while also putting in 60+ hours a week, and that if I’m not duly compensated… I quit, right now, full stop. I don’t know how much to ask for, since I suspect that if they actually are willing to negotiate, they’ll try to go the route of “We’ll give you a raise of $20,000/year” or something like that… but like I said, I have every confidence that their plan from the outset was to lay me off in a couple of weeks anyway, so that “raise” for 2 weeks of working would only net me like, less than a thousand bucks in that instance (although I guess it would look better on a résumé… but what I’m after right now is cold, hard ?compensation?).

Anyone who has any insight or tips for negotiating in a situation like this, please do share! How to play hardball, how to cover my ass legally, whether HR should be involved… anything and everything! Thank you for reading!