A court in Russia sentenced a dual citizen of Russia and the United States on Thursday to 12 years in prison on accusations that she committed treason by donating money — about $50 — for Ukraine’s armed forces.

The court, in the city of Yekaterinburg, claimed to have found that the funds donated by the woman, Ksenia Karelina, 32, “were subsequently used to purchase tactical medicine, equipment, weapons and ammunition” for Ukraine.

The prosecution nearly always gets its way in treason cases in Russia’s stage-managed judicial system, but her lawyer, Mikhail Mushailov, said he would still appeal to try to get her sentence reduced.

“I was not surprised by the prison sentence or the way the trial was conducted,” Mr. Mushailov said by telephone phone from Yekaterinburg.

The conviction of Ms. Karelina, also known as Ksenia Khavana, was the latest in a series of treason and other cases by Russia against citizens of Western countries. The surge in such cases in recent years has raised concerns that the Kremlin views the accused as valuable assets to be traded for high-profile Russians held by the United States and other countries in the West.

Mr. Mushailov said that in addition to appealing Ms. Karelina’s sentence, he would be “taking all the legally required actions” to make her part of any future prisoner exchange between Russia and the West.