As for whether or not she'd be willing to go on a double date with the pair, Richie, 32, said she "[approves] of anything that's going to make Benji happy."
"I am a devoted sister-in-law," she continued -- Richie is married to Benji's twin brother Joel Madden. "I'm happy for anyone who is happy, and I want everyone to be surrounded with love."
News of Diaz's relationship to Madden was first reported in May as the two had reportedly been "hanging out" a lot over the past few weeks.
Celebrity Breakups and divorces of 2014 [PHOTOS]