Here's why:
* Subject pronouns are used as the subject of a sentence (the person or thing doing the action). In this sentence, "Shalini" is the one doing the action of helping.
* Object pronouns are used as the object of a verb or preposition (the person or thing that receives the action). In this sentence, "us" is the object of the verb "help" because "Shalini" is helping "us".
Let me know if you have any more questions!