Joe Biden replied to a letter from the detained US basketball star Brittney Griner, in which she described fearing she would never return home from Russia, her wife told reporters on Friday.

“I was able to read [Biden’s] letter, and it brought so much joy as well as BG,” Cherelle Griner said, using a nickname for her wife. “I believe every word that she said to [Biden] he understood, and he sees her as a person, and he has not forgotten her, which was her biggest cry in her letter.”

She added that the Biden administration again made reassurances that it was “exhausting all efforts” to repatriate Griner more than four months after her arrest in Russia on drug charges.

Cherelle Griner’s remarks came a day after Brittney Griner, 31, pleaded guilty to drug possession and smuggling charges at her trial in Moscow. She had been detained in February at an airport in Moscow after agents allegedly found vape canisters with cannabis oil in her luggage.

The trial had started a week earlier, prompting growing calls for the Biden administration to do more to secure the release of the former WNBA, NCAA and Olympic champion. In her plea, Griner admitted to the charges but said she had unintentionally brought the canisters in question because she packed in a hurry.

Griner’s legal team in Russia has said it hoped the guilty plea headed off a severe sentence. She faces up to 10 years in prison, and the case is due back in court on 14 July.

Biden’s White House received a letter directly from Griner during the nation’s Independence Day celebrations on Monday. “I’m terrified I might be here forever,” said an excerpt that her representatives shared with the Guardian. “I realize you are dealing with so much, but please don’t forget about me and … other American detainees. Please do all you can to bring us home.”

Two days later, Biden called Cherelle Griner and assured her his administration was doing everything it could to secure Brittney Griner’s release. The president also followed up with the letter , Cherelle Griner revealed at the Friday news briefing.

The US state department considers Griner wrongfully detained, moving her case to an official who essentially serves as the federal government’s chief hostage negotiator.

Political tensions between the nations are high because of Russia’s decision in February to invade Ukraine, which has received billions of dollars in weapons and other resources from the US. And the administration has not made public any strategy that it may have to get Griner back from Russia.

Griner plays for the Phoenix Mercury, having helped the team clinch the WNBA title in 2014 and leading it to an appearance in the finals in October. During off-seasons since 2015, she has played for Russia’s UMMC Ekaterinburg, leading that club to three domestic championships and four continental titles.