I would think $30K as Casino mentioned is almost the best scenario for the niece.
If, assume that the niece is in a community property, pro-woman state (e.g., CA), she is entitled to half of the savings (and debts) during marriage, including 401K and house appreciation. As to down payment, unless the niece contributed to it, I don't think she could have half of it. Of course, she could try and her hu*****and might be stupid enough to agree to give it to her. As we all know how much house appreciated for the last two years, there won't be much money (if any) in it. Savings is probably quite minimum as they still have debts on credit cards. Not sure about the car though.
I do think the aunt wants too much for the niece; however, no harm to ask. But going through lawyer to get more property might not worth it. (Does not seem the hu*****and is very rich; so do not seem worthing trying.)