Figure out some way to jokingly embarass her in front of all her friends.
Like pop in with a wiggles DVD and suggest they watch it because my sister loves it and watches it every day. Or mention how she cant go to sleep unless i tell her a bedtime story or something.
thats what big brothers do. Embarrass the younger ones.
Like that one time my little brother was having a feats of strength contest with his friends and I lift him over my head yelling, WHERE'S YOUR TUTU, FAGGOT?