Moral dilemma

My grandmother's brother's wife died yesterday. I love them both greatly and I'm really sorry for him, they were married for over 50 years and they were like one. Funeral tomorrow in the town they lived, and I know I should be there... despite my social awkwardness and everything I want to be there. However, I need to pay school before the 4th to get early payment discount and I don't have the payment form yet. Even worse, I need at least 3 days to get the money from the bank so I'd need to get payment receipt tomorrow. This year hasn't been easy and we aren't in a good position, economically, so the discount would be very helpful...
And I don't know what to do. Convince mom we'll be alright despite paying more or feel like pomegranate for not being in the funeral, accompanying my granduncle.