Replying to Fat girls at dances

ii was at a school dance and i have a friend thats a girl and shes not the skinniest girl in the world. so when im grinding her friends and shitt shes just like looking at me and shes dancing alone. im like shitt she wants me to dance with her. by no means do i want to dance with her. what the hell do you do in that situation?! i felt reallly bad that she was just chillen there the whole night while all her friends and my friends were havinn a fun time