A good server wouldn't just take the damn money without clarifying what it's for. When I have people put a card and cash in a book, even if I'm already in the back, I will walk back out to the floor to ask them if they want me to use the cash and then put the remainder on the card. Most of the time, the cash IS my tip, but I NEVER assume.

And I'm sorry, but she's a butthole for running after y'all and saying that the $25 was DEFINITELY her tip. Even if she had taken the $8 out of that $25, $17 on a $60 tab is still a good tip.