A good quote will reflect the relationship between the two of you. Some examples are:
"She keeps me wild" and "She keeps me safe." — Unknown.
"A sister is both your mirror —and your opposite." — Elizabeth Fishel.
"Our roots say we're sisters, our hearts say we're friends." — Unknown.
"Sisters are like flowers in the garden of life." — Unknown.
"A sister is a forever friend." — Unknown.