A great plot could be a story where Roslin discovers a plot against Robb. She then has to find a way to warn him without being discovered. This could involve her using her family's connections and her own wits. It would be a story full of suspense and danger. Or, it could be a story set in an alternate universe where Roslin and Robb are able to escape the political chaos of Westeros and start a new life together in a far - off land, away from the wars and power struggles.
Well, a plot could revolve around Roslin trying to understand Robb's leadership and the difficult decisions he has to make. She could start as a bit of an outsider but as she gets to know him better, she becomes his confidante. For instance, when Robb has to decide whether to attack a certain stronghold or negotiate, Roslin could offer him a different perspective based on her understanding of the people involved. And as their relationship develops, they face challenges from those who oppose their union, which could add more drama to the fanfiction.
One plot idea could be Roslin and Robb meeting secretly during the tense times of the war. They could share their fears and hopes, gradually falling deeper in love as they realize they have more in common than they thought. For example, they might both be tired of the bloodshed and long for a peaceful future. Another idea is that Roslin uses her knowledge of the local area to help Robb in his military strategies. This would not only bring them closer but also show how their union could be beneficial for Robb's cause.