Have you told her how you and her son feel? Does she realize you both have expectations of her? Is she able to pay? How old is she? Is she healthy in body and mind? How many 'free rides' did she give her son? Does she have anywhere else to go? Not knowing these answers I wouldn't feel comfortable in saying "Give her the heave ho."
You gotta put her in a home.
Stick her in a home thats what I would do!
Failing that switch off the electric or put password on computer so she can't get on internet :-)
It's a tricky dilemma - do you watch CSI ?????