She is the only person still alive in Nepal who fluently speaks the Kusunda language. The unknown origins and mysterious sentence structures of Kusunda have long baffled linguists.
As such, she has become a star attraction for campaigners eager to preserve her dying tongue.
Madhav Prasad Pokharel, a professor of linguistics at Nepal's Tribhuwan University, has spent a decade researching the vanishing Kusunda tribe.
Professor Pokharel describes Kusunda as a "language isolate", not related to any common language of the world.
"There are about 20 language families in the world," he said, "among them are the Indo-European, Sino-Tibetan and Austro-Asiatic group of languages.
"Kusunda stands out because it is not phonologically, morphologically, syntactically and lexically related to any other languages of the world.
He warns that if the Kusunda language becomes extinct, "a unique and important part of our human heritage will be lost forever".
Even if some of the lofty intellectual arguments for preserving the Kusunda language are lost on Ms Sen, she is acutely aware of how its demise affects her personally.
"Fortunately I can also speak Nepali, but I feel very sad for not being able to speak my own language with people from my own community," she said.
"Although there are still other people from the Kusunda tribe still alive, they neither understand nor speak the language.
"Other Kusunda people... can only speak a few Kusunda words, but can't communicate [fully] in the language."
Ms Sen fears there will be no-one to speak the Kusunda language after her death.
"The Kusunda language will die with me," she reflects, while lamenting the failure of the government and academics to help transfer the language to the next generation.
Although no detailed figures are available, the Central Bureau of Statistics says that only about 100 Kusunda tribespeople remain - but only Ms Sen can speak the language fluently.
A few years ago, there were two other people - from a mid-western Nepalese village - who spoke the Kusunda language fluently.
They were Puni Thakuri and her daughter Kamala Khatri.
But since then Puni Thakuri has died and Kamala has left the country in search of a job.
Ms Sen - despite her age - still ekes out a living as a stone-crusher. But outside of the workplace she finds that she is increasingly in demand from linguistics students wanting to learn the Kusunda language with her help.
They are documenting it in a bid to keep this rare language alive.
Researchers have so far identified three vowels and 15 consonants in the Kusunda language.
Threat to tribe
The Kusunda tribe to which Ms Sen belongs is nomadic. As hunters and gatherers, they live in huts in the jungle and carry bows and arrows to hunt wild animals.
While the males of the tribe hunt, women and children stay at home and search for wild fruits.
The Kusunda - a short and sturdy people - refer to themselves by the word "myak" in their language. They kill monitor lizards ("pui") and wild fowls ("tap").
Linguists and tribal campaigners are now demanding that the government introduce specific programmes to uplift the Kusunda tribe and protect their language.
But no such policy is on the cards, at least in immediate future.
"We do not have any specific programme to preserve this language," admitted Narayan Regmi, spokesperson of the Ministry of Culture.
The National Ethnographic Museum had meanwhile conducted a study on 10 different Nepalese ethnic groups including the Kusunda.
Its research has reached a grim conclusion. The entire Kusunda tribe is on the verge of disappearing along with its last fluent speaker in Nepal.
Gautam, Bimal. 2012. "Nepal's mystery language on the verge of extinction". BBC News. Posted: May 12, 2012. Available online: http://www.bbc.co.uk/news/world-asia-17537845