(NewsNation) — Dual U.S.-Russian citizen Ksenia Karelina remains imprisoned in Russia after being detained while on a visit from Los Angeles.

Russian officials accuse her of supporting Ukraine and raising funds for a Ukrainian organization. On Thursday, a Russian court denied Karelina’s appeal.

Her boyfriend, Chris van Heerdan, told NewsNatino’s Chris Cuomo he feels “helpless” and “powerless” because he can’t do anything to help her.

“It’s a day-by-day thing because I never expected this,” Van Heerdan said on “CUOMO.” “I never imagined being in this situation.”

Van Heerdan received a letter from Karelina in which she revealed what prison conditions have been like.

In the letter to her boyfriend of six months, Karelina said she has to go to sleep with the lights on and that there isn’t any hot water.

“You get to go outside once a day to the rooftop, but it’s freezing. It’s cold, it’s snowing. And sometimes if you go up, they leave you out there for hours. … I mean, reading this from this woman is breaking my heart,” Van Heerdan said. “Why is she going through this? I’m desperate.”

The couple traveled to Turkey together before she continued on to Russia to visit family, but she was detained at the airport.

Ksenia Karelina is a dual U.S.-Russian citizen who came to the U.S. to study ballet and received U.S. citizenship when she married an American. The couple later divorced, and Karelina was recently working at the Ciel Spa in Los Angeles.

Karelina is currently being detained as a “preventative measure” during the investigation. If convicted of treason, she could face up to 20 years in a Russian prison.

White House national security spokesman John Kirby said the White House and the State Department were aware of reports of the arrest and added that “we are trying to get more information and to secure some consular access to that individual.”

The Associated Press and NewsNation’s Stephanie Whiteside contributed to this report.