Sarah Krivanek Facebook
"I am begging you to please act on her behalf," Anita Martinez wrote in a letter she says she submitted Aug. 10 through the White House website, a copy of which was shared with PEOPLE. "Do something to ensure that her basic human rights are being met and that contact is made so that we can send her the supplies needed to maintain herself."
In November 2021, Krivanek was charged by Russian authorities with "intention to inflict slight bodily harm" and "threatening to kill or do grievous bodily harm" following a domestic violence incident with a Russian man named Mikhail Karavaev.
In court, Krivanek alleged that Karavaev had abused her before and indicated that she was defending herself during the incident, which left him cut on his nose by a knife.
She was released on bail after agreeing in writing that she would not leave Moscow and would demonstrate good behavior until her trial. But on Dec. 15, she was arrested at a Moscow airport while trying to catch a plane to flee back to the U.S.
Krivanek carried with her at the airport a letter that showed she received a $200 repatriation loan from the U.S. government to cover expenses on her journey to the States. She also reportedly secured a diplomatic escort to the airport.
A State Department official previously told PEOPLE that the agency was aware of the December 2021 arrest of a U.S. citizen but said the American Embassy was not aware that she was ordered to stay in Moscow until her trial. She's now serving a one-year, three-month sentence related to the assault charges.
"I am quite aware that Sarah may have to serve out the duration of her sentence before we can get her home," Martinez wrote to President Biden. "My concern is the lack of communication and I worry about her well-being and mental state of mind as we do not know her current living conditions."
"Based on his description of what the conditions are like in Russian prisons, I am even more concerned for Sarah because we've not been able to send her supplies through their inmate commissary website, a phone number is needed on Sarah's end," Martinez writes.
Sarah Krivanek Facebook
"I fear that since Sarah has had nothing for over 8 months that she may be suffering from malnutrition. Even the official Russian government prison site recommends sending cartons of cigarettes to use as currency," the letter continues. "Sarah has absolutely nothing to bargain with, I fear for her health and safety due to potential mistreatment because she is an American Citizen!"
In her letter to Biden, Martinez included information on Krivanek's whereabouts that she received from Russian human rights activist Ivan Melnikov.
"Please sir, as an American Citizen who loves and respects my country, I am begging that you please help me help my friend," Martinez wrote in the letter's closing. "I do not want her coming home in a body bag because nothing was done by our government to help her survive."
Martinez had not received a reply from the White House by Friday afternoon.
The White House did not respond to PEOPLE's request for comment on Martinez's letter to Biden.
However, after emailing a similar letter to the U.S. Embassy in Moscow, Martinez did get a reply. Citing privacy concerns, the embassy did not comment on Krivanek's specific case but said, "Please be assured that the consular section at Embassy Moscow is doing everything it can, with the constraints forced upon it by the Russian government, to assist all of our citizens incarcerated in Russia."
Melnikov has also written a letter, which PEOPLE has reviewed. His message to Sec. of State Antony Blinken was also submitted through the White House site Aug. 4 and describes the circumstances of Krivanek's case.
"I do not believe," he writes, that "Ms. Krivanek represents a danger to society."
Sarah Krivanek Facebook
He also says that he "firmly believes" Krivanek should be a "potential candidate in the ongoing negotiations on prisoner exchanges between Russia and the United States."
"I have no doubt that the Russian authorities will be willing to support such a humane initiative," Melnikov tells Blinken in his letter.
Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer.
Last week, American WNBA star Brittney Griner was sentenced to nine years in prison following her trial in Russia for alleged drug smuggling.
"Russia is wrongfully detaining Brittney," President Biden said in a statement after the sentence was announced. "It's unacceptable, and I call on Russia to release her immediately."
Griner is now the subject of discussions on a prisoner swap between the U.S. and Russia, and Melnikov's letter implies that he hopes Krivanek's fate will also be considered.
But Griner's and Krivanek's cases are different, according to Chris Costa, a 34-year veteran of the Department of Defense and former U.S. Army Intelligence officer who is now the executive director of the International Spy Museum.
Unlike Griner, Costa does not believe that Krivanek is considered by the U.S. to be "wrongfully detained," based on criteria laid out in the Levinson Act.
Facebook; KIRILL KUDRYAVTSEV/AFP via Getty Sarah Krivanek and Brittney Griner, two Americans jailed in Russia
"She is a victim, but she might not be a wrongfully detained, that's a category," Costa told PEOPLE in an interview last week. "She was defending herself, but that doesn't mean she's wrongfully detained in accordance with Russian law."
Costa added that the status of Krivanek's detainment "does not mean that the United States is not working on ensuring that she has all of what is entitled by a U.S. citizen in terms of Consular support."
He also emphasized that a determination of whether a prisoner is wrongfully detained based on the Levinson Act is likely ongoing and could certainly change over time.
"It's an analytical judgment based on the facts of the case. But it's kind of a sliding ruler based on the situation. It's dynamic, too, because new facts can come to light and political environments can be revealed," he said.
Letters written on Krivanek's behalf could help, given the intense coverage in the media of Griner's case and the outpouring of support for her and calls to bring her home.
"Sarah's family could be optimistic that the United States is really redoubling," Costa told PEOPLE. "We are committed to taking care of U.S. citizens held abroad wrongfully."