The 37-year-old TV personality, one of musician and record producer David Foster's five daughters, confirmed in August that she is engaged to Simon Tikhman.
When asked at the MIRROR Westfield Century City grand opening event on Tuesday if other members of the family, like Katharine, will perform at the wedding, Erin told E! News, "Yes, 100%. They're free, are you kidding? Right? It's free built in entertainment."
"So Kat wrote me the other day, she was like, 'Is there anything that I can be doing to help you prepare?'" Erin continued. "And I said, 'Yes. Vocal exercises. Prepare your voice because you will be performing.' She's like, 'OK'...there's a song from Waitress that we really want her to perform that we really love. I don't know what else. Yeah, just anything. She truly has such a beautiful voice. Simon and I are real fans of her so I'm very excited."