Does diegetic music from a live event invade copyright?

Ok, so I'm making a video of a wedding. It's a promotional video for the designer who provided the jewelry. At one point, all of the bridesmaids start dancing to Prince's 'I wanna be your lover'. Even though the bit is only about 13 seconds long, I am afraid of invading Copyright and getting the designer in trouble. The whole video is about 3:30 and we would really like to include the girls dancing in the video. Does anyone have a definite answer to whether or not diegetic music invades copyright? Even if the girls are singing over it? It's a really fun, upbeat bit, and the girls are really having fun. It definitely doesn't hold any negativity.