I would like to preface what I say, with, I dont post very often, as by the time I get to a thread everyone has already said mostly what I would like to say, so you can take my words with the weight that they deserve.
I am truely sorry, most posters are unable to take you at face value when you say you and your mother can not afford anything. I understand that people are trying offer alternative suggestions by saying well such and so is JUST $5 or what ever amount, but you have stated that you did not budget for this unexpected event and there is NO extra money to be had. The board (in general) all the time seems to get on other people for always offering up other suggestions when you already stated that you can not do something.
I do however think the offer of time to do something IF that is possible for you is a good alternative. Otherwise, I think you should just go and enjoy seeing your aunt. 5 years from now after your dear aunt has departed, you will know you got to enjoy seeing her, and I am sure she will enjoy seeing you and your mom. I doubt you will be worrying about if you brought food for the party or not.
I am sorry that you are losing a loved one. My condolences to you and your family in your time of need.