What does your lease say? Is it a fixed dollar amount? Then you have no right to see the bill. Is it a set percent? Ask to see the bill – and allow her to redact any personal information.
Before you do this ask yourself if it’s worth the potential discomfort to discuss this at all? Could savig $5, $10, $15 be worth it?
Also see if pepco can give you the average usage over the past year or so.