I took it that Marlena just thought it funny that rich and snooty Giselle was so insistent on having Roman as her date, or she would not donate any artwork up for auction. She knew Roman agreed only "for the cause", and was enjoying the joke with him.
However, calling Giselle by other names was showing how unimportant that woman was to Marlena. Sami DID do the same when speaking to Lucas of Autumn a couple years back.
Giselle herself, in my opinion, was very snooty, and rude to everyone. She had to have her toy, or she was going to take her goodies home in her limo, and she did not care how stranded everyone else would be.