I don't get why she is so popular, it's like the Biggins effect, someone that is large, talks in a shrill posh voice and bangs on about being fair.
Roesemary purposely dropped Brian in it, she knew exactly what she was at, she's not silly, and got the camp to shoot the messenger.
Rosemary also purposely winds up Hugo, aided and egged on by Nadine, who hasn't been able to stand Hugo since day one.
Rosemary is also jumping on the 'Helen has a game plan' bandwagon that Nadine trotted out. Note how Colin was cagey about it, yet Rosemary leapt straight in to announce that Helen is very clever, and agree with Nadine.