The three other derailed fuselages that did not go into the river are still on site or nearby, she said.
The cause of the derailment is still under investigation, she said.
The fuselages were being shipped from the Spirit AeroSystems plant in Wichita, Kansas, to a Boeing facility in Renton, Washington, to be assembled into airliners.
The huge blue-green fuselages are a common site on railways along the 2,000-mile trek from Kansas to Washington state. Ken Evans, senior manager for Spirit AeroSystems, said the company ships 42 of the 737 fuselages each month.
Spirit AeroSystems has been designing, building and shipping the fuselages by rail from Wichita since 1968, he said.
"In my memory, we've not had a serious derailment like this before," he said Monday.
The toppled hulls have become a spectacle for rafters to gawk at as they float past the partially submerged hulls on the Clark Fork River.
Jason Shreder, owner of Zoo Town Surfers located about a quarter-mile up the river, told the Missoulian that a few people booked raft trips over the weekend to see the fuselages and other debris from the derailment.