Spectre is a hard carry. Late game she can tank up and stay alive while the enemy team dies to Radiance, Dispersion and Images.
To play the hard-carry aspect up to the fullest, you need to go for a radiance rush. That said, it requires a huge amount of allied support to pull that off well against a decent team. As a result, a more gank-oriented strategy that fills into a carry role later is generally more advisable.