One-handed typer here – well, one hand and one finger, and it’s been like this for all my life. Your friend may want to consider text macro tools such as Keyboard Maestro for macOS. There are many others, but KM will also launch apps and do other magic for me just by typing two or three letters. Create a list of frequently used words or segments, define a generic expansion key (in my case #) that doesn’t require a modifier. I have more than 1000 of these macros, and it really helps with all those long words in my native German. Dictation may also help, although I find that it leads my thoughts in different directions when I see words appear on the screen as I speak.