Possible Clues:

• 'I Kissed a Girl' singer
• 'Firework' singer
• "I Kissed a Girl" singer
• Singer of 'Rise' and 'Roar'
• Singer with over 100 million Twitter followers
• World's most-followed Twitter user, as of 2018
• Pop music superstar
• "Roar" singer
• 'Roar' singer
• Pop star who twice voiced Smurfette