Charge admission to a party?

Dear Limo Princess,
My brother and future sister in law often throw parties at their house for their friends. We talked about having a bbq there for the holiday weekend and I offered to bring whatever they would like, all she needed to do was tell me beforehand. The night before the party I received a text message stating that there would be a $15 a person charge to attend. This is not the first time she has charged for dinner but since she hasn't tried in a while I assumed she had thought the better of it. I think it's tacky and am offended. Granted, they did put in the money for the food and beer, but we would have happily brought our own beer and made or brought anything that would be asked of us. Even if they had asked us to help front the bill earlier than the night before it wouldn't have been so offensive. I am considering not attending and unsure if it is my place to bring it up to her that asking people to pay a cover to come to your house is crass. I am concerned however that left unaddressed this will be a recurring issue in our relationship. I don't want to offend but I also don't want to be resentful or find excuses why we cannot attend. Is there a way to emerge from this gracefully?

Dear Reader,
I had to read your question three times and I am still horrified that someone could be so incredibly loutish as to use a social situation as an economic enterprise. Your FUTURE sister-in-law is in desperate need of a remedial course in social graces. I am convinced she was raised by wolves that were living behind the trailer park. It is about 23 light years PAST uncouth to charge someone to come to your home when they are there by your invitation--it is just simply NOT DONE--and I am amazed that ANYONE would attend anything at her home. Most certainly you should not attend this event and as for being worried about offending her I don't think it's possible for you to offend anyone who has the absolute gall to charge people for accepting an invitation. She is beyond being offended by anything short of human sacrifice and I'm wondering about that! There is NO SITUATION where charging people to attend a social event to which they were invited to is acceptable--NONE!! It is absolutely totally socially unacceptable in any situation to do this and your brother should really reconsider marrying this woman if he wants to keep his friends and family on speaking terms with him. The only socially acceptable way to share the cost of a social event is to ask people to bring a dish of whatever you ask them to make. I've hosted potlucks which are a lot of fun because I call it a recipe exchange which everyone loves because they get to taste a lot of things and get the recipes for ones they want to make in the future. There's a name for parties people are charged to attend, they are called fundraisers. People DO attend them by invitation but know they are expected to pay to attend from the beginning, they are for whatever cause and are tax deductible. Your way out of this is to tell your crass, rude and totally socially unacceptable future sister-in-law that you only attend fundraisers for causes that are tax-deductible. This will leave her speechless and baffled and might possibly clue her into the fact that she needs to learn social graces. With any luck she will do this immediately and spare your poor brother the lifetime of embarrassment that marrying this woman will heap on him. What will happen when he invites his boss for dinner? Will she present him with a bill at the end of the evening? It's too horrible to think about the many ways this woman will socially ostracize him, but perhaps he will come to his senses and insist she learn manners.