Is a woman's voice considered 'awrah if she sings Islamic songs in front of men at a wedding?

The basic principle is that a woman's voice is not awrah (something that must be concealed), but it is forbidden to listen to it if it is accompanied by softening or alluring tones, due to the Almighty's saying: "then do not be soft in speech [to men], lest he in whose heart is disease should covet." Softening the voice and melodizing it with anashid (chants/songs) can incite fitnah (temptation/strife). Therefore, it is not permissible for a woman to perform anashid in front of non-mahram men, nor is it permissible for them to listen to her, whether the anashid are Islamic or not.