She is the youngest of 4. And you are so right, she really doesn´t "have" to talk, because everyone understands her. That´s exactly what I told her kindergarten when they asked me whether I was worried about this.
She understands almost everything and follows directions very well. If I ask her to get her ball, doll, pacifier, blanket etc. I can also tell her to put something in the trash can, put her doll to sleep in the stroller, go and get a diaper and so on without problems. She points to things and bodyparts (eyes, nose, mouth, ears, hair, tongue, belly, fingers, toes and bum) when asked.
I keep reading that she should have a vocabulary of 50 words by the time she´s 24 months and that she should be talking in 2 word sentences by then. I only recall 1 of the other 3 children having been able to do that.