I guess you could also call this a 4-Strand Braid but it seems more like weaving to me.
Her hair is still wet because we were rushing out the door to a primary activity and had to do something very fast. She wanted to incorporate one of her "colors" in her hair today. You can pick these up at Sally's in tons of colors and they're about 18 inches long. (You can cut them if they're too long for your princess's hair.) They have a little comb at the top of them that slides right into the hair or you can combine it in an elastic like we've done. The weave is made by sectioning the ponytail into 3 strands with the colored hair being your 4th strand. Simply take the 4th strand and weave it over and under the other 3 strands. Continue weaving back and forth until you come to the end of the hair. This looks really cool with your 4th strand being normal hair as well.
This style took less than 5 minutes and she was out the door.