Throwing this link up again because they do good courses for helpers. The financial planning one does involve teaching various ways of saying "no" to other people asking them for money.
There is nothing wrong that your house helper asked for a salary advance. in fact, if shes' really did her job at her best, then there's no doubts you'll have to refused on her request. But be sure she really really needs it or she's telling the truth why she's asking an advance for her salary.Two of you needs to trust to each other.