The artist’s career was remarkable partly because it was so _____: she died, with only a few paintings to her credit, while still in her twenties.

The situation here is that her career was partly meaning to some extent or short (this is my first guess)

Then I read further and notice the colon.
After the colon it's the explanation of the blank: she died when she was in her twenties, so she only has a few paintings.
Therefore, her artist career was short.
The only word that works in this blank is abbreviated

felicitous means pleasing and fortunate or appropriate
prolific means plentiful - this would contradict after the colon
enduring means lasting over a period of time – this also contradict
conventional means normal – nothing in the sentence suggests this