I am with your daughter on this, jeni - babies cry for a reason and I would be very unhappy if one of mine had been left to cry. I can't give you the source, but I heard a news item recently saying that some research had found that babies who were left to cry had more emotional problems in later life.
Practically, can she tell the childminder how she feels, and will her opinion be accepted? Was there any logical reason for the baby to be left so long (7 minutes is a long time). Is the baby looked after in your DD's own home? If so, could she install some covert equipment to monitor what happens?