Unfortunately it's not her nipple. It's just part of her dress.
That's what I thought when I saw the 2 older pics but it's hard to tell for sure without more proof. Her publicist said she was wearing a cover underneath or something so I believed that for a while but then again that could also just be PR damage control. Most people seem to think it's a nipslip instead... so idk, unless we have pics from the designer of the dress or something that shows the inside.
Top 15: Taylor Swift, Selena Gomez, Emma Watson, Bella Thorne, Elle Fanning, Chloe Moretz, Hailee Steinfeld, Kendall Jenner, Emma Roberts, Victoria Justice, Gigi Hadid, Ashley Benson, Ariel Winter, Debby Ryan, Hayley Williams
Total over analyzing here but it looks like it could be nipple but there seems to be absence of areola. So either the angle and light obscure said areola or she just has very light areolas. OR that is not a nipple. But I want to believe it is a nipple!