In a very real sense, Sela is Spock's Romulan counterpart: of mixed ancestry, born to a prominent Vulcanoid male and a female human of no standing within the Vulcanoid society where they were raised, as adults they both were exceptionally talented individuals capable of achieving things on a galactic scale. Sela arguably surpassed Spock in this, becoming an actor for Romulan galactic interests in her 30s.
(I've argued
here that the plot in "Reunification" for the invasion of Vulcan actually makes sense if you assume--as has been established in the novels--that there's some pro-Romulan sentiment on Vulcan. That planet's High Command had been sockpuppeted by the Romulans in the 22nd century, after all, and an arrogant Romulan elite might well believe that Vulcans wanted to be reunited.)
The critical problem for Sela, sadly, was that her society was much more repressive than Spock's. Spock's mother was able to find her way on Vulcan as a free individual; Sela's mother was a general's chattel, executed for trying to escape with her child. Romulan racism is certainly orders of magnitude more severe than anything on present-day Vulcan; Sela did well to achieve everything that she did.
Sela's life was distorted by these hatreds, alas, inculcating a toxic self-hatred that expressed itself in repeated attacks against the Federation. Her life was ultimately ended at the pinnacle of her achievements by this hatred, when as Chairwoman of the Tal Shi'ar she authorized--against the Praetor's express wishes--attacks on the Federation. She ended up taking her life rather than be extradited to the Federation. Sela could never step away from being the young girl whose scream in the night led to her mother's execution.
