This poem's called "Power," so it's pretty much a given that it's going to be about power in one way or another. One of the big questions of the poem is: what's the definition of power? Is power about knowledge? Physical strength? Is power about influencing others? About inspiring others? All of these are possibilities, and we can definitely answer "yes" to more than one of these questions. But no matter how we (or the poem) define power, one thing's for sure: Marie Curie was a pretty powerful lady who had a huge influence on this history of science.
Power is of the body; Marie Curie was only powerful when she was alive. Now that she's dead, her power has disappeared.
Marie Curie's power lies in her lasting influence upon generations of scientists. It doesn't matter that she's dead, and that her body decayed; her power lives on.