I want to host a family dinner and make a peanut dish so my sister can't come because she is allergic.
Why wouldn't you want your sister to come to the dinner?
She is trying to get money out of me all the time for her pet causes.
If your sister needs help and wants to contribute to a worthy cause, you should be more understanding and donate what you can. You should be generous with your money when you can help a charity and give to the needy.
I don't like her anyways. She is so annoying.
Your sister only wants to help others and she doesn't have enough to make the contributions needed to these charities. You have an obligation to help her since she is family and not contributing puts her in a difficult position. Make a contribution and help her out.