The sentence that contains a nominative absolute is "Her hair blowing, Emma ran through the field with her kite".
The nominative absolut part is: HER HAIR BLOWING". This part of the sentence is a noun phrase that begins the sentence and it has no grammatical connection to rest of it.
Nominative absolutes can be found at the beginning or end of a sentence -and in some cases in the middle- but in this particular case it is found at the beginning.