My DP's old neighbour had 3 young children (none of them over the age of 3). She regularly went out clubbing at night leaving the 3 kids home alone. Eventually one night someone called the police (well several people did) and the children were taken into care.
There were other issues of neglect though, but the fact was that night the children were removed from the home as they were classed as being at risk. They wer not returned for other reasons which came out in the investigation that followed.
You really do need to let someone know what she has told you.