This is the second acid attack on the woman, whose eight-year-old rape case is about to go to trial.
When her train arrived in Lucknow on Thursday morning, she reportedly went to the railway police and, unable to speak, wrote about the attack before being rushed to the hospital.
In a brutal assault in 2008 allegedly over a property dispute, the woman was gang-raped at her village in Raebareli and acid was thrown on her abdomen. Three men were arrested then. "Acid was poured on her private parts," said Minister Rita Bahuguna Joshi, holding up the case as an example of lawlessness on the previous Samajwadi Party government's watch.
Ms Bahuguna alleged that the woman, a Dalit, had begged for security but the Akhilesh Yadav government didn't help her.
As the week-old BJP government targeted its predecessor, Chief Minister Adityanath declared Rs 1 lakh compensation for the woman and ordered the police to arrest the attackers at the earliest. By the evening, the police had made two arrests.
The woman's family says it has received constant threats over the years as part of aggressive attempts to force them to withdraw the case.
The latest attack on the woman took place when she was returning after a visit to Unchahar, around 100 km from Lucknow, where her husband and children live. She works at a cafe in Lucknow that employs acid attack victims, and had gone to her village for her daughter's class 10 exams.
"The Chief Minister told me strict action would be taken and that is what I want," said the woman's husband, who had dropped her off at the station. "...I am a poor man but still pursued the case because I believe in my wife."
Rita Bahuguna Joshi said, "There was no hearing of the case for years. The woman had been fighting for justice for a long time. We have been in charge for a week and we will not tolerate all this.