The couple quietly tied the knot in September after a whirlwind summer romance.
"They’re perfect for each other because they're like the same person," Ireland Baldwin, 23, told People on Saturday. "They're both really sweet. They complement each other. They’re both very loving of each other."
Ireland says Bieber, 24, and Hailey, 22, find common ground in their mutual struggles with fame.
"They're going through the same struggles, I feel like, and they are just helping each other out," Ireland explained. "As life goes, we all go."
Though the couple are already legally married, reports recently suggested that the Biebers would host a blowout wedding to celebrate their marriage with family, friends and God, but Ireland insists she has no details about any upcoming party for the pair.
"We're happy. We're going to the wedding," Ireland said of her famous brood. "We don't know when it is or where, but we're happy for them."