The participial phrase running after her dog is made with the help of the present participle of the verb run and functions as an adjective modifying ‘she’.
A participial phrase consists of a participle, modifiers and complements.
Running after her dog is a participial phrase consisting of the participle running and the prepositional phrase <em>after her dog, </em>which includes the preposition <em>after,</em> the object of the preposition <em>dog</em>, and the possessive adjective <em>her</em>.