The most common verb to use with "tip" when you're at a restaurant is "leave", not "pay":
Did you leave her a tip?
How much did you leave?
You use "leave" because the normal way of giving a waiter a tip is to leave the money on the table when you leave the restaurant. In other situations, like when you are tipping a taxi driver, you "give" instead:
I gave him a five dollar tip.