Tomar, 28, died en route to a hospital here in the wee hours.
She is survived by her husband and two sons.
"Sunita came to us (Mumbai) around seven days ago for treatment, but she insisted on returning to her native place in Bhind district in Madhya Pradesh since her two kids were alone," Pankaj Chaturvedi, who treated her at the Tata Memorial Hospital in Mumbai, told PTI.
"Around three days ago she returned to Bhind and last night her condition deteriorated. She complained of breathlessness after which she was taken to a local doctor, who referred her to a Gwalior hospital, but she died en route," he said.
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She shared her experience in a video, which was used by the government for its anti-tobacco drive to warn people against consumption of smokeless gutkha and pan masalas.
Just a few days ago, she had written to Prime Minister Narendra Modi expressing deep disappointment at BJP MP Dilip Gandhi's statement in his capacity as chairman of Lok Sabha's Committee of Subordinate Legislations that there was no Indian study to confirm that tobacco use leads to cancer.
"Recently Dilip Gandhi, chairman of a parliamentary panel wrote to the Health Ministry asking for the notification on bigger tobacco pack warnings to be kept in abeyance. I was shocked that people in such high posts can be so irresponsible.