Talking to a child when they ask recurrent questions ...?

My wifes step sister had a child and after 2 weeks the father was shot and killed. Now she is a single mother and we have to babysit here and there. This little girl gets thrown from babysitter to babysitter ... she is now about 4+ and was told her father is in heaven ... but she keeps asking me (a 45 year old childlesss man) what happened to her daddy while we are watching her ... I finally (being an overly honest and straight forward type) told her a bad man shot her dad and I said it in a soft and caring voice. Well, months later she tells her mom that her dad was shot and that I told her ... her mother is now furious with me ... should she be? The baby is a result of "revenge " where the mother was in a fight with her alchoholic boyfriend and went to a bar and found an old friend (who I hear was a drug dealer) and had with him and then 2 weeks later he is mysteriously shot to death ... and now she is mad at me for telling her little girl ... what is your opinion please?