#1 Compliments about her intelligence. As much as girls like to be told they’re pretty, calling her smart is a much more effective way to make her feel good. If she’s beautiful, she’s probably always complimented on her looks. But what about her brains?
#2 Compliments about her creativity. Aside from just being smart, girls love to be told they’re creative. It’s not a compliment people usually give and that’s why it’s one of the things girls like to hear. They don’t hear it often so it means more.
This is even more powerful when used during a time she’s actually being creative. So if she just painted something or made a bracelet or something that involves creativity, just tell her she’s very creative. It’ll make her day.