In 2013 France's Council of State upheld the refusal of local officials to grant Agathe Habyarimana residency papers on the grounds that she was a "danger to public order".
Her lawyer Philippe Meilhac claims the refusal was political discrimination.
"Several of my client's children are in France, some having French nationality," he said. "An unfavourable treatment is being applied to Mme Habyarimana for political reasons because diplomatic relations must be maintained with Rwanda."
The 71-year-old woman has taken the case to the European court, claiming that the refusal is a breach of the European Convention on Human Rights.
Agathe Habyarimana, a Hutu, is accused of being one of the planners of the 1994 mass murder of Tutsis and non-sectarian Hutus that followed the fatal shooting down of her husband's airplane.
A French court in 2011 refused to extradite her to Rwanda to face genocide and crimes against humanity charges but an inquiry into charges of complicity with genocide is ongoing in France.
The French military brought her to France shortly after her husband's death and she applied for political asylum after deciding to live here in 1998.
The application was unsuccessful so she applied for residency papers in 2009.