Diaper shower/party

Anyone ever had one instead of having a baby shower we have bought everything this go round for our daughter. Im having a diaper shower Saturday and confused on whats the real difference im wanting to help my sister in law shes throwing it but i dont know what i should get i told her i would get a punch bowl and drinks and stuff and a 'its a girl' cake made and all but she told me to just get cupcakes instead. Its stressing me out. I'm bot sure what i should get or what all you need for one because technically its not a baby shower its a diaper shower please help thank you.