"Heidi looked amazing," she told MTV News after the ceremony in Pasadena, Calif. "She was wearing a million dollars worth of diamonds over a strapless Monique Lhullier dress."
Even though Heidi and Spencer kept their composure during the ceremony, Stephanie said she couldn't help but get emotional.
See photos of Heidi and Spencer's Mexican wedding
"I was up there, and her back was towards me, so I don't know if she was crying," said Stephanie, who was a bridesmaid. "But she was getting mad at me if we would start crying so that she wouldn't start crying."
Spencer and Stephanie's parents -- who were among the 200 guests -- also "were very emotional, like most parents would be," she said.
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Heidi's sister, Holly, was maid of honor and "really kept it together," Stephanie said. "Everything worked out great."
As for Spencer? "He was really good," Stephanie said. "He was really happy."
Unlike their trip to Mexico last year, Heidi and Spencer's ceremony Saturday was "with the family," Stephanie said. "There was a legal priest, and the ceremony had prayers. It was completely different."
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After the wedding, the bride and groom joined friends and family for two receptions at Social Hollywood and the Beverly Wilshire Hotel.