Vanessa Trump was being examined at New York-Presbyterian Weill Cornell Medical Center as a precaution, according to cops.
The suspicious letter was sent to Trump Jr.'s apartment in Manhattan this morning, police said. Emergency medical services, firefighters and police were called to the apartment just after 10 a.m. after Vanessa Trump opened the letter, police said.
She and two other people at the apartment were decontaminated by firefighters at the scene before being taken to the hospital, according to cops.
"The substance was deemed to be non-hazardous and is being transported to a lab in New York City for further analysis," said NYPD spokesman J. Peter Donald.
Secret Service was also investigating, the NYPD said.