It's important to recognise that only the first week of college has happened - firstly a knife scar with stitches would take a while to heal, and longer to fade into scar tissue, second, if Sasha was attacked by someone with a knife and needed a bodyguard following her around college and to social events, it is definitely something quite recent - everyone else knows the gossip but Nika and Nami, because they are new to the social circle. No one else would need to ask.
At least, that is how I understand it - if (as Fun Shaundi thinks, and I think is likely), it is something to do with the married man who tried to seduce her, the jealous wife whatever, that makes a lot of sense. That's why the gossip is still going on at the book club, because it's still something new and gossip worthy.
The weirder one is that Nika must be an alien to have a scar heal in basically a day, or Ocean decided the scene where Nami teaches him to use concealer on it too controversial
I also think it will be part of her signature look - Ocean isn't consistent with wounds, as Vic would likely still look like a car hit her, unless the mysterious time dilation happens between scenes with no 'meanwhile' or 'one month later...' frames inbetween.
About scart and contrast, a port wine birthmark would have been epic. But it really depends on why the scar is there as to what Ocean wants to tell - he'll need the scar to remain until he explains it at least, otherwise we'll forget that's part of the story, a visual cue to remind us of the past events.
