what happened to that rich lady jack made a deal to marry?

Rose did have her killed. If you remember, when the prince and his future bride were about to make their entrance for the press, and we were all thinking ti would be Jack and Katrina, suddenly Jack appears with the little brunette idiot. The man standing next to Rose in the receiving line, as they're all applauding Jack and his new fiancee, says to Rose, "it was so unfortunate to hear what happened to katrina!" and Rose replies, "Oh, I know....but anyone who would risk driving those winding mountain roads to Antioch...."

Katrina had just told Rose in a previous scene that she was rushing off to Antioch to buy a gigantic engagement ring there. Katrina had been bragging to Rose that she was going to be queen and was going to relegate Rose to the position of "royal granny", so Rose saw her chance and had Katrina bumped off.