This is just basic DJing. Works best with funky stuff, especially if they drop vocal bits in the intros.
It really comes down to song selection. She’s got two tracks playing at the same time, one is the more basic beat outro, and the other is her new track with the “everything I do” bits. Since both aren’t too melodic or anything, this works. From there you just drop the volume quickly on the vocal track, and then slam up the volume on the points you want dropped in.
If you’re looking for music like that, check out the deep house and tech house sections on the mp3 stores, and even the “Jackin” section on traxsource.com.