Although Nurse initially helped Romeo and Juliet, after Romeos banishment she advises Juliet to marry Paris and forget Romeo. Why does Nurse most likely do this?

Paris is the easier option. At first, Nurse encourages Juliet's infatuation... she's like an indulgent mother. When everything goes wrong, Nurse changes her mind and encourages Juliet to take the safe route. Romeo is banished, Juliet is in her charge, and she is an employee of the Capulets. Marrying Paris would keep them both out of trouble.