Complex sentence: From there she travelled north through Sweden and Finland to reach Russia, joined the Russian flying ambulance service headed by Prince and Princess Peter Volkonsky, tended to the wounded in Łódź after it was bombarded, and then nursed in and around Warsaw.
Split into simpler sentences: From there she travelled north through Sweden and Finland to reach Russia, joined the Russian flying column, or mobile medical unit, headed by Prince and Princess Peter Volkonsky. As part of this unit she tended to the wounded in Łódź after it was bombarded, and then nursed in and around Warsaw.