Final answer:
The phrase 'The past behind her' is a prepositional phrase that functions adverbially in the sentence to provide context about the position of 'the past' in relation to 'her'.
Step-by-step explanation:
The phrase "The past behind her" is a prepositional phrase. This type of phrase typically starts with a preposition (in this case, 'behind') and includes a noun or pronoun that is the object of the preposition ('the past'). Prepositional phrases can function in different ways within a sentence, such as adjectivally (to describe a noun), adverbially (to modify a verb, an adjective, or another adverb), or as a noun phrase.
In the example given, the prepositional phrase is acting adverbially, giving information about the location of 'the past' in relation to 'her'. Prepositional phrases are common in English and help to provide additional context within sentences.