"I'm gonna vomit!" she told the Web site after hearing the news Tuesday. "I so didn't need that info ... Yuck!"
The actress, 23, and Michael, who turns 50 on April 25, have recently engaged in a very public war of words. She lashed out at him on Twitter for years of bad parenting, while he urged her to go back to rehab.
Major, 27, who was previously romantically linked to Jon Gosselin, told People magazine that no date has been set for the wedding, but "it will probably be in New York, probably at the end of this year."
Michael Lohan told the magazine, "I'm ecstatic. I've never met anyone who's been there for me like Kate. She's always been there for me. The one thing about Kate is that she doesn't come with baggage."
Major, who was wearing an engagement ring Tuesday, said she was "ecstatic" about the impending nuptials.
"I'm ecstatic. I'm very happy. Michael and I have known each other for four years, and it's meant to be."