I'm guessing that the papers are radioactive through exposure to her, and so that would mean her actual body is even more radioactive still. Is this correct? If I took a Geiger counter to her grave, would it pick up higher than average radioactivity?
According to this article from the British Society for the History of Radiology on her & Pierre Curie's exhumations in 1995 (to be transported to the Panthéon), her body was buried in a lead coffin & was slightly but not significantly radioactive (compared to background levels) when the coffin was opened.
Pierre Curie's remains, however, had a significantly higher level of radiation. This is thought to be because he died in a traffic accident & so died at a much younger age than Marie. Therefore, he had less chance of eliminating the radioactive radium from his body over time through biological processes.
The article mentions in particular that Marie Curie would have suffered postmenopausal osteoporosis (loss of bone mass), which would help eliminate radium that built up in her bones. She also worked with radium less later in her life, & adopted more protective measures.
Pierre Curie was not buried in a lead coffin, however, because there was less understanding of the dangers of radiation when he died in 1906 compared to Marie Curie's death in 1934.