Gerunds in a sentence functions as a noun. Hence in a sentence, a gerund will act as direct objects, subjects, subject complements, an object of prepositions or indirect objects. Every gerund ends in -ing, and so does present participles. On the other hand, present participles act as modifiers or complete progressive verbs.
Therefore, in the above sentence, "Susan has learned gardening from her aunt."
Gerund 'gardening' is used as a direct object of the verb learned.