Party ideas for a 13 yr old girl?

so my sister asked me 2 plan her 13th bday but im not the kind of person who does parties even 4 myself so im drawing a plank any ideas? plzz help anything. i think its gunna b a sleepover so yah kk plzzz help its all girls last yr she had a grl boy but this yr she wants just girls so yah any ideas...nothing way way expencive