What should I wear to this Bat Mitzvah?

This is my 1st bat mitzvah and my 2nd mitzvah in total- I have no idea what to wear! It's my best friend's and it's in June at a nightclub immediately following services. I don't need something with sleeves because I have basically every colored shawl you can imagine hahaha. The problem is I am skinny and petite, only 4'8'' and 13 years old, and I am very preppy and conservative, so I won't wear leggings, sparkles, sequins, anything with a super low neckline, really bright, bright colors, or anything short enough to wear with jeans and still look good. I also don't want to look like an old lady, so I don't really like too much lace or frillyness, and no more than an inch lower than the knee. Thank you so much! As you can see I am having some trouble with my conservative style, size, and limited experience! Thank you SOO much for all who help!!!