Sometimes if the party is 8 or more, the gratuity (usually 15-18 percent) is automatically added onto the total bill balance. So if the party was 8 or more, the gratuity would have been included in what they owed and therefore the waitress would have been correct.

However, if there was no added gratuity due to it being a large party I don't see why any waitress would demand a 25 dollar tip on a 60 dollar bill LOL. Something doesn't sound right there.