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.

....ask your mom?

....ask your mom?

She just got here. Left her phone this morning and we couldn't talk at all during day.

Update: We decided I'd stay here and get the receipt. My receipt isn't ready yet which annoys me greatly, I'll have to talk with university people to see if I still get the discount because it's not my fault the damn thing isn't ready. I had to stay here feeling like crap for nothing... We talked in the afternoon and it's so damn heartbreaking.