This is very clearly explained in the MGMAT SC
Samantha's - is a possesive noun
She - is a possesive pronoun
The rule says: Subject and Object pronouns may not refer back to possesive nouns.
They can only refer back to Subject and object Nouns
Here Samantha's is a possesive noun, so we cannot use 'she' as the pronoun. It is better to use Samantha again to make it clear.