She also said she could not "hide my opinion" when grilling Pallett following her departure from the show, although she tries not to share her views with the audience.
-> Christa Ackroyd: How Roxanne Pallett has let me and other domestic violence victims downFormer Emmerdale star Pallett claimed that Thomas had deliberately hurt her with a punch in August, which viewers defended as play-fighting.
She later walked from the show and apologised for making a "massive, horrible mistake", while Coronation Street star Thomas received overwhelming support from the public.
CBB presenter Willis told The Mail On Sunday's You magazine: "Thank God there were cameras, because it could have ruined Ryan, such was the gravity of the situation."
She was praised for her "steely" post-exit interview with Pallett, but Willis said: "To me I was just having a conversation about something that was really serious.
"Sometimes we do have light, fluffy chats about people in the Big Brother house and then sometimes really serious s*** happens in there and you've got to be able to ask the questions everybody is thinking."
On not showing sympathy for Pallett, Willis said: "I've never tried to impose my view on the audience, but when something like this happens, something that felt so wrong, I couldn't hide my own opinions."
Since the punch row, Pallett has left social media and quit her job as a co-host on Minster FM's breakfast show.
Ofcom received more than 25,000 complaints about the allegation of physical abuse and has launched an investigation.
Thomas later said that he feared he would have to face the police over Pallett's allegation.
He told This Morning: "I just felt like, the police were going to call me, it was serious and that's why I broke down because I was so, so frightened."