Boss wants employee to train their outsourced replacement who will be earning 75% less: '[He] expects me to train her...'

There's this weird thing that happens in employment, you're there to get a paycheck—no question about that. And while your employer will want to pay you (close) to market rate if they want to keep you they're always going to want to pay you as little as they possibly can get away with. You want more, they want to pay less, probably figuring that they'll get the same amount of work out of you regardless. This dynamic will hang over any employment agreement you enter into.

There becomes a point though where respect comes into play—ask for too much and your employer might feel (or act) disrespected—get paid too little and you're going to be feeling the same. Treading that middle ground is delicate but of penultimate importance for the continued working relationship.

Without a doubt, learning that your job is going to be outsourced internationally for 75% of the rate would come as a shock and make you feel disrespected. Having your boss subsequently ask you to train that outsourced replacement would probably go over like a lead balloon.