As much as you or your mom doesn't want to hurt w, please realize that by not saying/doing anything or paying for it.. you aren't LOVING her, you are ENABLING her.
How about you and your mom come to a few options that is safe for your mom? Make sure your mom (not you) is completely comfortable with those options.
Then talk to w and discuss those options. Let her know the consequences if she does nothing and express your concerns.. not that you are worried about her.. that she will miss out on her kids' lives!
Give her some time to decide (that is still safe for your mom) and then let her make the decision.
Try to do it as loving as possible without coming to rescue. She may get mad, but you're right.. there are consequences to all actions.
My .02
M(f): 40 D'ed: 8/12
Show empathy when there's pain. Show grace when warranted. Kindness in the midst of anger. Faith in the face of fear.