BY ALL MEANS CALL CPS ... !!!
DO IT RIGHT NOW AND WITHOUT DELAY ... !!!
This mother is out of control and could very well end up killing this child.
You can contact their 24 hour hotline and let them know what your friend has told you she's seen, heard and observed.
They'll send someone out to assess the situation and take appropriate action.
You can remain anonymous if you so desire.
AGAIN ... BY ALL MEANS CALL CPS ... !!!
AND DO IT RIGHT NOW ... !!!