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 Paul 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.
"It's not often you get to work with someone for so many years and he was so exemplary in the way he lived. Paul Walker was more beautiful inside than out," Brewster added.
'Fast & Furious 7' is scheduled for release on April 10, 2015 in the US.