No. Fiza Ali does not sing. She is the performer/actress. The vocalist is solely Mazhar Rahi.
If you specifically need the MP3 file (perhaps to put on a USB drive for a DJ who doesn't have internet access at the venue), you should purchase it legally. Wedding Sehra Mazhar Rahi Fiza Ali Mp3 Download
This emotional mix is why the song is played during the Rukhsati (farewell) as well. here is the iconic opening:
For those searching for the Sehra lyrics to print for a wedding ceremony, here is the iconic opening: Wedding Sehra Mazhar Rahi Fiza Ali Mp3 Download