Is it fair to divide a will inequally among adult siblings if one is much more needy.?

2 of the daughters have good husbands that have secured them a retirement, etc. Their husbands are retired, they live well (new cars, trips,etc.)The third daughter had the misfortune of having a husband that left her at age 54 with no pension and she can't find work in this economy.She worked hard getting training but no one will hire her because of her age, etc. She is now 60 and I have had to help her with surviving for years. Should my will be divided 3 ways with what I've paid her taken out of her third to give to the other 2 daughters. (They have seen the accounts of what I've given her). They feel that she shouldn't get anymore than they should. I feel that because of her unfortunate cirstances that she shouldn't have to "pay back" her needed help. What do others think of this situation when one family member has had to endure many difficult cirstances??