At what bank / branch was it?
I would be hard for an employee to steal $700 just like that given the number of cameras that are now in place in most banks.
If he gets caught, the employee would not only lose his jobs but have a criminal record.
I see two possible explanations:
1) you friend didn’t count right at the first place. She counted $2100 when it was in fact $1400.
2) her sister is the one who tricked her.