Nasus's E not blocked by Sivir spell shield

I was playing an ARAM playing Sivir. They had an AP Nasus and I wanted to block his E burst damage using the spellshield. I know that Sivir cannot block DoT (like Cassiopeia's Miasma) but I would think that Sivir would be able to block his instant burst damage from Nasus's E when he puts it down. I don't know if this is a bug or not, but I think Sivir should be able to block his E burst.