Production on the sequel was halted last year when Walker and his friend Roger Rodas were killed in a car crash, reported Digital Spy.
"I haven't been to set yet, but I imagine it's going to be very difficult," Brewster said.
The 33-year-old actress also spoke about the impact that Walker has had on her life, given that they starred in multiple 'Fast & Furious' movies together.
"I just remember seeing this stud walk into the room the first time and he had this bleached-out hair. I met him as a baby and I saw him grow into an awesome, amazing, charitable man.
'Fast & Furious 7' is scheduled for release on April 10, 2015 in the US.