i have recommended "Get a financial life: finance for your 20's and 30's" to a few friends who were in about the same boat as your trainer, very limited finance knowledge, but very readable. The first chapter summarizes all the other chapters, then she can read the other chapters at her choice or interest. It covers a wide variety of topics like debt, savings, car loan, mortgage, retirement savings, ect.
Then i would advise her to read "your money or your life" which is more on the frugal side and teaching the concept of financial independence.