My son attended a private party at Maggiano's and I was very impressed with the set up they had. Very nice room upstairs and the service seemed very attentive.
On the other hand, my in-laws (who are very sophisticated and experienced diners) were recently at a private luncheon at Biaggi's and came away with raves.
I'd also consider the type of food the restaurant serves. I recently hosted a baby shower and even though the guest of honor has very adventurous tastes, she had found that her tastebuds (and digestion) had modified in her last trimester. If you haven't already, I'd suggest that you double check with your guest of honor as to whether or not her tastes have changed.