The top model (29) decided she had to hire one to help her and her businessman partner with their two ceremonies as there is “just so much to think about”.
The couple are planning ceremonies at home and abroad with some “guaranteed sunshine”.
The pair are planning on tying the knot next June.
She told the Irish Independent that she’s currently going over the “little bits and pieces”.
“I don’t know how brides do the whole thing themselves, there’s just so much to think about. Every day there is something new,” she said.
“At the moment, we’re discussing what kind of paper to use for the invitations, all those little decisions that seem big at the time.”
Rosanna was speaking at the Fashion Lunch, which took place earlier today in aid of the Dublin Rape Crisis Centre.
The Fashion Lunch for the DRCC has been taking place for the last 18 years, and has helped raise some €2m for the cause.
Virgin Atlantic were sponsoring the event, and “checked in” the glamorous guests.
Bride-to-be Rosanna looked beautiful in a plunging floor-length gown by her designer friend Dawn Fitzgerald.
Following her appearance in US Playboy two weeks ago, the former Miss World said she would consider posing naked again but only if she was able to control “every aspect” of the shoot, as she did with the Playboy photographs.
“It would freak me out to do the shoot and then not know what photos were going to be used until the day it came out,” she said.
“When it’s something as intimate as your body you want to have control over what you show.”
The lunch was hosted by Celebrity Apprentice contestant Amanda Brunker and Miss Candy.
Speaking about the upcoming TV3 series, former Miss Ireland Amanda said viewers can expect to see a lot of “ugly crying” from her during the show.
“They didn’t go any easier on us because it was the celebrity version; in fact I think they went harder.
“I’d say it’s going to be entertaining viewing, but I won’t be able to watch it,” she said.
Other guests in attendance included Lisa Duffy, Virginia Macari and model Rebecca Maguire.