My mother almost consistently uses "while" when she means "until", and vice versa. (This is because in her native language, those are the same word.) Obviously, I can't simply tell her, "whichever word you were about to say, choose the other one", because that would just make her second-guess herself all the time, even when she happened to choose the correct word in the first place (see above about almost consistently). What I need is a mnemonic or other device that will unequivocally help her determine the right word to use in a given situation.
Does anyone here teach English to native speakers who encounter this issue? What device or trick can you suggest for keeping these two words straight?