Question: What Native American language was Jane Hassler Hill extensively working on?

Context paragraphs:
Uto-Aztecan languages: Uto-Aztecan or Uto-Aztekan is a Native American language family consisting of over 30 languages.  Uto-Aztecan languages are found almost entirely in the Western United States and Mexico.  The name of the language family was created to show that it includes both the Ute language of Utah and the Aztecan languages of Mexico.

Koasati language: Koasati (also Coushatta) is a Native American language of Muskogean origin.  The language is spoken by the Coushatta people, most of whom live in Allen Parish north of the town of Elton, Louisiana, though a smaller number share a reservation near Livingston, Texas, with the Alabama people.  In 1991, linguist Geoffrey Kimball estimated the number of speakers of the language at around 400 people, of whom approximately 350 live in Louisiana.  The exact number of current speakers is unclear, but Coushatta Tribe officials claim that most tribe members over 20 speak Koasati.  In 2007, the Coushatta Tribe of Louisiana, in collaboration with McNeese State University and the College of William and Mary, began the Koasati (Coushatta) Language Project as a part of broader language revitalization efforts with National Science Foundation grant money under the Documenting Endangered Languages program.

Indigenous languages of Arizona: Arizona, a state in the southwestern region of the United States of America, is known for its high population of Native Americans.  Arizona has the third highest number (and the sixth highest percentage) of Native Americans of any state in the Union (See Demographics of Arizona).  Out of the entire US population of 2.9 million Native Americans, roughly 286,680 live in Arizona, representing 10% of the country's total Native American population.  Only California and Oklahoma have more Native Americans than Arizona by number.  Arizona also has the highest proportion of land allocated to Native American reservations, at 28%.  Arizona has five of the twelve largest Indian reservations in the United States, including the largest, the Navajo Nation, and the third-largest, the Tohono O'odham Nation.  Also, Arizona has the largest number of Native American language speakers in the United States.

Jane H. Hill: Jane Hassler Hill, (born Frances Jane Hassler, October 27, 1939) is an American anthropologist and linguist who has worked extensively with Native American languages of the Uto-Aztecan language family and anthropological linguistics of North American communities.

Cheyenne language: The Cheyenne language (Tsėhésenėstsestȯtse) or, in easier spelling, "Tsisinstsistots", is the Native American language spoken by the Cheyenne people, predominantly in present-day Montana and Oklahoma in the United States.  It is part of the Algonquian language family.  Like all Algonquian languages, it has complex agglutinative morphology.  This language is considered endangered but at different levels in both states.

Stanford American Language Institution: Stanford American Language Institution () is an early childhood and primary (K to 12) educational institution based in Taiwan.  Mainly located at Hsinchu City, Hsinchu County, and Miaoli County, subsidiaries include: Stanford American Language School (史丹佛美語學校) (include: kindergartens, nursery schools, and buxibans) and Stanford American Language Press.  Stanford American Language Institution is the single largest private provider of English education in the county of Hsinchu and Miaoli.

Klamath language: Klamath , also Klamath–Modoc and historically Lutuamian , is a Native American language that was spoken around Klamath Lake in what is now southern Oregon and northern California.  It is the traditional language of the Klamath and Modoc peoples, each of whom spoke a dialect of the language.  s of 1998 , it was spoken by only one person.  As of 2003, the last fluent Klamath speaker in Chiloquin, Oregon was 92 years old.  As of 2006 there were no fluent native speakers of either the Klamath or Modoc dialects.

Lakota language: Lakota ("Lakȟótiyapi"), also referred to as Lakhota, Teton or Teton Sioux, is a Siouan language spoken by the Lakota people of the Sioux tribes.  Though generally taught and considered by speakers as a separate language, Lakota is mutually intelligible with the other two languages (cf. Dakota language), and is considered by most linguists one of the three major varieties of the Sioux language.  The Lakota language represents one of the largest Native American language speech communities in the United States, with approximately 2,000 speakers living mostly in northern plains states of North Dakota and South Dakota.  There is a Lakota language program online available for children to use.  There is also a Lakota Language Program with classes for children at Red Cloud Indian School.

Washo language: Washo (or Washoe; endonym "wá:šiw ʔítlu") is an endangered Native American language isolate spoken by the Washo on the California–Nevada border in the drainages of the Truckee and Carson Rivers, especially around Lake Tahoe.  While there are only 20 elderly native speakers of Washo, since 1994 there has been a small immersion school that has produced a number of moderately fluent younger speakers.  The immersion school has since closed its doors and the language program now operates through the Cultural Resource Department for the Washoe Tribe.  The language is still very much endangered; however, there has been a renaissance in the language revitalization movement as many of the students who attended the original immersion school have become teachers.

Mono language (California): Mono is a Native American language of the Numic group of Uto-Aztecan languages, the ancestral language of the Mono people.  Mono consists of two dialects, "Eastern" and "Western".  The name "Monachi" is commonly used in reference to Western Mono and "Owens Valley Paiute" in reference to Eastern Mono.  In 1925, Alfred Kroeber estimated that Mono had 3,000 to 4,000 speakers.  s of 2010 only about 40 elderly people speak Mono as their first language.  It is classified as critically endangered by Unesco.  It is spoken in the southern Sierra Nevada mountains, the Mono Basin, and the Owens Valley of central-eastern California.  Mono is most closely related to Northern Paiute; these two are classified as the Western group of the Numic branch of the Uto-Aztecan language family.

Supporting paragraphs: Jane H. Hill Uto-Aztecan languages
Answer: Uto-Aztecan or Uto-Aztekan