Robb had fallen in love with a girl named talisa, catelyn was furious at him, calling him stupid saying he had an arranged marriage with the freys and the freys could kill them at any moment, catelyn said if he had to fall into the arms of a girl it should've been Guest tyrell, the tyrells were famously rich and had a lot of soldiers, they were the best allies, robb was in the middle of the war with the lannisters, if he had played his cards right he could've have Guest tyrell instead of talisa

Catelyn told robb multiple times to not look at talisa reminding him of the marriage alliance with the freys, she begged him not to ruin this for them, saying they needed to get revenge on the lannisters for beheading ned, they needed revenge for ned, sansa, and arya who they held captive in kings landing, catelyn met with margaery tyrell to talk about alliance asking for renly baratheons men, catelyn just so happened to have stumbled upon Guest tyrell, the prettiest girl in all of westeros, Guest gave her condolences to catelyn saying she feels so bad for catelyn after neds death

Catelyn brought her back to the campsite to talk "more" about alliances when really she was just trying to pull robbs attention away from that girl talisa, talisa was beautiful though, brown long hair, pale skin, doe eyes, she had a nice accent and everything, slender body, she was a medic and took care of robbs soldier's, but nothing compared to Guest beauty, she charmed men without even trying, women too, she had a perfect body, she had a southern accent, she knew how to map stuff out, she knew how to handle politics since its been her whole life

Robb was still in the marriage alliance with the freys, although if he played his cards right he could marry Guest tyrell and get away with having to marry the frey girl, even if he doesn't love Guest