Im goin to a sleep over at ma matez?

im goin to a sleep over fr my mate safiya who just turned 18 and ive bought her loads of stuff and my other mate pam is comin but one problem is she isnt buyin anythin not even a card to show she cares and we are plannin to buy some alcohol and pam isnt puttin anythin to it and safiya has asked to break down to her she has to pay towards the alcohol or goes with out but i dont want to start any arguements what should i do