Attack the Moon widow

Since Swan Song doesn't really know any attacking spells yet, so she decides to instead keep her distance and support the other ponies that actually can do some damage to the Moon widow. She casts a mist spell to make it harder for the giant spider to see the other ponies, as well as light spell to blind the beast temporarily to it hinder her even more, from seeing any of Swan Songs allies attacking.

Then however she gets an idea.

 She remembers the ice spell that Frostbite used at the very beginning of the fight and uses her magic to throw one of the ice spikes he created at the spiders face, wich causes the spike to impale one of the spiders many eyes.