I would suggest it for the safety of D13, and her safety as well. Suggest it to D13 and mention how much fun it would be for she and her mom... Manipulative, I know, Im out of ideas on that one, but I do think that it would be good for both of them.
Do you make her car payment, cell phone, any of that? Stop it. Do you have a joint bank acct? I would suggest splitting that up and asking her to be responsible for some of the household bills. Im sure that after nearly 20 years of marriage she doesnt have a very realistic idea of how expensive it would be for her to live on her own.
I guess I gave the wrong finger to the wrong man...