The mother's name may be on the mortgage but is it on the title?   Even though no rent is paid, it is possible that, depending on the Province, these freeloaders may have some legal rights.  If and when this enabling parent decides to pull the plug, she should first consult a lawyer to avoid any problems.  The daughter should be offered help but not a free ride.  She must get a job of some kind and dump the jerk or no help should be forthcoming.
Nothing will change until the mother stops all this foolishness which seems unlikely so forget worrying about a situation over which you have no control.