Ask for cab money.
Wait, didn't you pay for the drinks last night, and provide her with some quality humping? Just kidding. But seriously, how's she gonna demean herself by asking this question? If you offer, you're a gentleman. If she asks, it kind of makes the whole deal a paid transaction. No, it doesn't make it better if she asks you to put it in the pocket of her pants in the other room instead of in her hand. The sleight of hand is only part of what makes this exchange ultra awkward.