Is it permissible for a mother in need to care for her mentally and physically disabled 40-year-old son in exchange for money?

It is permissible to serve and care for a man who has no desire [for women] and no knowledge of women's affairs, provided that there is no fitnah (temptation/disorder) in it. This is analogous to the ruling concerning a doctor, for whom it is permissible to look at and touch [a patient] to the extent of need, with a preference for avoiding direct touch by using gloves and the like.