I have a customer that can't have crisco/shortning in their icing. She thinks that is what makes her daughter sick when she has cake and icing. I need to make a fondant cake next week. I am trying to decide what type of icing to use under the fondant. I have never used SMBC or all butter buttercream. I live in Houston so it has been humid here lately and in the 70's. Cake will be picked up on a Thursday for a Saturday party.
SMBC-can this be used under fondant and sit out for 3 days? Will it melt? Also, to apply the fondant to the cake do I cover with fondant while icing is chilled, and if so do I just spritz cake with water to attach? All butter-again with this be okay sitting at room temp for 3 days or will it melt? Do I apply fondant to cake while buttercream is chilled or at room temp.

I haven't worked with either of these. I usually do all crisco or crisco/butter combo. Does anyone have any suggestions on what will be best and if so how to accomplish a nice fondant covered cake using non crisco buttercream. Cake is for next week so need any help I can get. Thanks!!!!