What would you do?

My mother-in-law is like the little boy who cried wolf one time too many.
As a consequence no one believes her any more when she is in need of money.
Well she wanted my daughter to call her and it turns out she wanted to borrow 100 dollars to help with medical bills. So she says. My daughter said yes but she lives pay check to pay check.
She thought it funny that she didn’t ask us. My husband would give her the money gladly if she needed it but we have learned to ask for proof.
Too many times (especially this time of year) she would scam family members for cash for trips and gifts that no one needs.
Funny thing is she would get it if she asked up front but she always comes up with some sad story that ends up not being true.
She will ask several members not to say anything so they won’t all find out they are all helping to fund her next trip to California or Florida or to Japan. Or to pay for a 300 dollar phone for her favorite grandchild because his mom won’t buy it and this will make her look awesome in his eyes.
Anyhow, my daughter knows she can’t lend her the money because one, she needs to borrow it from us to begin with and two she would forever be an easy mark by her grandmom.
However, she doesn’t know how she can get out of it and not feel guilty for telling us.
Any suggestions on how to handle an old con woman who happens to be your grandmother.