At the time people didn't really understand just what radiation was or the dangers of it. Her death (sadly) helped increase our knowledge of radiation and its dangers.

One point of view is that Marie Curie was aware of the risks involved and went ahead anyway:

Marie Curie tended to deny the perils of radiation, despite being deeply troubled by the deaths in the 1920's of colleagues and radiation workers from leukemia.

Marie Curie's decades of exposure left her chronically ill and nearly blind from cataracts, and ultimately caused her death at 67, in 1934, from either severe anemia or leukemia. But she never fully acknowledged that her work had ruined her health.

Her daughter, Irene Joliot-Curie, and son-in-law, Frederic Joliot-Curie -- also Nobel Prize winners -- continued her work with radioactive material. Eventually, both also died of diseases induced by radiation.

But by all accounts Marie Curie was so intent on her research that even if she had recognized the risks there is no reason to believe she would have done anything differently -- or that she necessarily should have, given her achievements.