Petito was in constant contact with her parents and sibling during the trip, the suit said, and their last communication with them was on August 27.
Petito’s remains were found in Teton County, Wyoming, in September, a little more than a week after her family reported her missing.
The 22-year-old woman died by strangulation, the coroner ruled.
Laundrie returned to the couple’s home on September 1 by himself, left again roughly two weeks later and disappeared.
Laundrie’s remains were later found in a Florida nature preserve and a medical examiner ruled he died by suicide.
Nearby, authorities found a notebook in which they said Laundrie claimed responsibility for Petito’s death.
“As a direct and proximate consequence of Brian Laundrie’s tortious conduct, Nichole Schmidt and Joseph Petito incurred funeral and burial expenses, and they have suffered a loss of care and comfort, and have suffered a loss of probable future companionship, society and comfort,” the suit said.
Ms Schmidt is asking for a trial by jury, and although the lawsuit does not list a specific monetary amount, it does ask for “damages which exceed US$30,000 ($42,384)”
The Laundrie family’s attorney downplayed the suit in an email to CNN on Saturday (US time).
“The filing of the wrongful death lawsuit by the Petito family was fully expected,” Steven P. Bertolino, an attorney who represents the Laundrie family, told CNN.
“This lawsuit will most likely not be defended and the Petitos will have gained nothing more than a piece of paper that tells them what everyone already knows, which is that Brian was responsible for Gabby’s death as indicated by the FBI.”
CNN has reached out to Schmidt’s attorney but did not hear back Saturday.
Petito’s family also has filed a lawsuit against Christopher and Roberta Laundrie, alleging they knew their son Brian murdered Gabby Petito and were working to help him flee the country, CNN previously reported.
In an email in response to the earlier lawsuit, Mr Bertolino said he was confident the case would be dismissed.
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