I would stick with Burger King, but don't make a big deal of the ice they are going out of the way to give you the free ice. Asking for more of something that you get for free which they don't normally do is not a good idea. And while everyone makes mistakes, it sounds like the cashier was blaming you for the mistake and was rude about her mistake. If you were making a big fuzz about her making a mistake then I can understand her attutide because you were expecting her to be perfect. If you were polite to her then she should not have gotton mad at you for her mistake.

Also you can try making your own sandwiches. I don't think it is a good idea to go to Mcdonalds twice a week.(unless you are just getting drinks and salad). They probably know your car and face by now:D Maybe that cashier knows you and your friend well and is glaring at you because of your friend's ice demands everytime she goes. Ice isn't free for them so take what they give.