She met Frodo first, danced and flirted a bit .. then talked to Sam and fell almost instantly in love.
He's still at the "maybe she could be a friend" stage, and she's seeing hearts. And she's settled in to being Frodo's friend. They even danced a bit while Sam slept one night.
So, I had her hang out a bit more, talk, flirt, dance ... then Frodo gave her a back rub. Sam pictured thoughts of the two of them together and cried. Then I told him to "compliment" her, and he slapped her. She left.
After that, Frodo and Sam's love/friendly scores stayed at 100, but "kiss" was no longer in their menus for each other. I only got it back after an awful lot of talking, hugging, gift-giving, and other assorted grovelling on both their parts.
I'm playing Rosie now, and her scores for both Frodo and Sam are much higher than their scores for her:
Frodo to Rose: 43
Rose to Frodo: 58 (friendly)
Sam to Rose: 36
Rose to Sam: 79 (love)
The tentative plan is to get Sam and Frodo's scores a bit higher now. Maybe if they like her better, they won't get jealous of flirting with her. I hope.