The low wage earner is 100% able bodied but if financially reliant upon her husband....her husband is twice her age and now an elderly man, he has adult children from another marriage plus children with the woman (mentioned here). He want to divide his estate among all his children and his second wife. Which means there is very little financial security assuming he dies before her.
So her mother (of 5 children), who is currently dying, is wanting to give her the entire estate for future security, and has considered her other children are 'doing ok'. Hope that makes sense.
Did the mother pay for things like college tuition for the children? Did she give any of them money to do things like buy a house, etc?
The problem I see with giving the 5th child all the money is that I would worry that she would use it to help support her husband and comingle the money so that he gets his hands on it. If I had a child in that situation, I would but that child's inheritance in a trust with rules on how and when she can use it.
Also, I would advise the child to look at the inheritance laws of her state. If there is a will that gives money to his ex and the children, she can probably contest it since it cuts her out. Does her husband have retirement? Is it set up for her to get his retirement after he dies? She will also get his social security after he dies. If she is low enough income, she will also qualify for Medicaid and for income support, food stamps, etc.
She might be in a better situation than her mother knows.
I'd either give to the children equally, or divide it by 6 and give that one child 2 portions at most. But I would not give it all to the one child who has not taken care of herself. She made bad choices. She will continue to make bad choices with her inheritance if there is no protection like a trust.
How do the other 4 treat the 5th child? Would they help her if she needed it?