Whether itr need to be filed

u can filr nil if no income 

individual(age below 60)
Return filing is compulsory only if your income exceeds Rs. 2,50,000 

age >=60<80 the Rs. 300000
age >=80 then Rs.500000

so your cousin total income exceeds basic exemption limit then return filing is compulsory.. other wise no need to file( if cousin have interest can file nil return) and there is no restrictions for filing nil return

if the employer had deducted tds then it is advisable to file return and claim refund.