You need curl definers, if she's biracial, chances are i do not think her hair will become a 4b, maybe a 3c, or 4a, but it also depends what her hair type is. I am biracial also, and my hair is a 3b,3c what I use is mixed chicks. Its amazing and really enhances curls.

Section her hair, And put mixed chicks, OR a curl defining cream in her hair by sections. DO not touch when it is wet or it causes frizz for that "poof" look.

Hope this helps, good luck