In chapter 8 how does Marquette cause the Marquis’ dearth?

Marguerite had "inadvertently" caused the death of the Marquis,

"Twenty-four hours after the simple little ceremony at old St. Roch, she had told him the story of how, inadvertently, she had spoken of certain matters connected with the Marquis de St. Cyr before some men--her friends--who had used this information against the unfortunate Marquis, and sent him and his family to the guillotine."

Marguerite did have much to hate about the Marquis.Her brother Armand was nearly killed, "valets of Marquis de St. Cyr, and ignominiously thrashed--thrashed like a dog within an inch of his life-- for simply admiring his daughter." Still, "Marguerite, horrified at the terrible consequences of her own thoughtlessness." I'm really not too sure how terrible she actually felt. She really hated the guy. Sometimes I'm apt to read a bit of sarcasm in that last quote but she did, evidently, attempt to help him.