Su

Su
 

Hi,

Eso significaba que en el infinito cosmos que la rodeaba, su
padre y su abuela estaban tan presentes como cualquier otro astro; que era posible
su regreso.

Su regreso means their return, not her return. Are there any grammatical clues to help distinguish these pronouns? It's quite uncomfortable to search the context and tax your common sense every other sentence :)

This pronoun could be used in ambiguous fashion if not careful, but here it is supposed that the antecedent is both of the people established in the previous sentence (su padre y su abuela). Context is key (always depend on it).