According to this article
Bell, seen above, said her notation on the receipt was a “lapse in judgment that has been blown out of proportion.” Despite scratching out the tip added to the bill, Bell claimed that she left a $6 tip in cash, adding that she subsequently discovered the 18 percent gratuity had been charged to her credit card.
Well, yeah. That's because her bill wasn't for $34.93, it was for $41.22. Crossing it out on the receipt shouldn't allow you to pay less for what you agreed to pay. 18% gratuity was a stated requirement of parties of a certain size on the menu, if she didn't agree to that she shouldn't have ordered food. You would expect someone who goes to Applebees on a weekly basis (the articles states it was a frequent post-services meal for members of her church) to know that.
Like I said earlier, it'd be like trying to pay less for a tank of gas. Really, it'd be like trying to pay less than the stated price for ANYTHING.