Police said that the woman died in Thörishaus, a village southwest of Bern, as parts of the country were hit by a deluge.
In the nearby town of Köniz, 200 firefighters worked throughout the night to deal with flooded streams and landslides, evacuating several homes.
Landslides blocked the railway between Bern and the western city of Fribourg and between Montreux and Zweisimmen, while flooding cut the line between the capital and the town of Thun, Swiss Federal Railways (SBB) said.
Buses were pressed into service to provide alternative transport between Bern and Fribourg.
SBB said InterCity and InterRegio trains between the two cities will likely not running until 2pm on Monday.
Flooding also caused disruptions on the Bern-Thun rail line.
Flooding also forced the closure of several roads in the region, national road company Viasuisse said.
Bern and Fribourg were hit by heavy rain that began on Saturday and continued non-stop until midnight.