Previously, Ina had not wanted to admit the truth because she did not want Wang Yu to worry about her. Now, seeing Wang Yu so certain, she realized she could no longer hide it and decided to tell the truth.
As for the black night clothes, she had two sets, one stored in Lin Xi's bedroom and another in a suitcase at the hotel. The set she wore when she killed Crippled Wolf was the one from the hotel. After the deed was done, she threw the clothes away.
Wang Yu had overlooked this point and had forgotten that Ina had not brought any luggage with her the night before.