With the 16" MacBook Pro (2019) Apple is returning to the scissors keyboard mechanism; that is a tacit admission that the butterfly mechanism was a flawed design. Basically all Mac notebook computers with the butterfly keyboard qualify for the keyboard replacement program, another wordless admission that Apple's decision to switch to this design was ill considered.
A few years ago I replaced my aging 11" MacBook Air (2013) with the 12" MacBook (2017). I hated the latter machine's keyboard and replaced it when the 13" MacBook Air (2019). The Air 2019 has a modified butterfly keyboard but feels better than the appalling MacBook 2017.
Unhelpfully, you do not mention what she needs to do with her computer so it's impossible to make a relevant recommendation. You also neglect to mention a budget. That's like asking "which car should I buy?"
Assuming she does mundane work (office suite, mail, web browsing) any of the current models should be adequate. If she plans to keep the device for a long time, she should forget about a used machine.
Her best course of action would be to go to an Apple Store and try them all out herself.
If she does not need to buy the computer immediately, it might be worth waiting to see if Apple announces any new products this month. With the current coronavirus scare, this might be done via a press release rather than at a live media event.