My 5.5 yo son is in speech therapy for L, R, Th, Sh, and something else I can't remember. Developmentally, your dd is not behind - L is a tough one for some children, and ages 5/6/7 are the time to master them. I thought L was tough for all children, and laughed at my choice of names for my daughter (Ellen Lorraine L____), since neither of my children could say her name properly. But then I heard a 3 yo say some L words perfectly and saw that different children develop those sounds at different times. The speech therapist said R is the toughest to master, and I am seeing that.
Just keep an ear on it, and if it's still happening around 5 you may want to consult a speech therapist.
Leslie, mommy to DS (5.5) and DD (3.5)