From Timothy Snyder's book Bloodlands, from the chapter on the period when the Soviets and the Germans had split Poland between them by agreement. Each side was intent on removing the educated class of Poles in order to subjugate the population more easily.

In at least two cases, the Soviet terror killed one sibling, the German terror the other. Janina Dowbor was the only female among the Polish officers taken prisoner by the Soviets. An adventurous soul, she had learned as a girl to hang glide and parachute. She was the first woman in Europe to jump from a height of five kilometers or more. She trained as a pilot in 1939, and enlisted in the Polish air force reserve. In September 1939 she was taken prisoner by the Soviets. According to one account, her plane had been shot down by the Germans. Parachuting to safety, she found herself arrested by the Soviets as a Polish second lieutenant. She was taken to Ostashkov, and then to Kozelsk. She had her own accommodations, and spent her time with air force comrades with whom she felt safe. On 21 or 22 April 1940, she was executed at Katyn, and buried there in the pits with 4,409 men. Her younger sister Agnieszka had remained in the German zone. Along with some friends, she had joined a resistance organization in late 1939. She was arrested in April 1940, at about the time that her sister was executed. She was killed in the Palmiry Forest on 21 June 1940. Both sisters were buried in shallow graves, after sham trials and shots to the head.

[my emphasis]