If you're getting together with friends or having a party and you find yourself going back and forth with "Should I invite this girl? Should I not? Will it be rude if I don't?"

INVITE HER. And, if you're sitting in the lunch room or standing in a group and you notice a girl by herself, and you're thinking, "Will it be weird if I ask her to join in?" ASK HERITO JOIN IN. It's better to be a little weird than rude. Just include them.