This is the 12280th most frequent Russian word.
испуганной
"Испуганной" means "scared" or "frightened."
The word "испуганной" functions as a participle in the instrumental case, agreeing with "будучи" to describe the state of the dog.
Собака стояла, будучи испуганной громким грозовым раскатом.
The dog stood, being frightened by the loud thunderclap.
Here, "испуганной" serves as an adjectival participle, modifying "она" in the nominative case, indicating her emotional state.
Она выглядела испуганной, когда дверь внезапно открылась.
She looked frightened when the door suddenly opened.
In this sentence, "испуганной" is used in the dative case to describe the girl who received help.