After the initial business with her, you can drop it and move on. There are other resources that can help Carol's situation. But Sasha is probably the most potent way to make sure Carol's situation improves. Sasha also is probably the best chance to get an almost full harem (you cannot have both Roxy and Natalie, but otherwise I think everyone will eventually be possible). She would be more like the one to keep things together once the MC "assembles the team", to use a poor turn of phrase. At least, that's how it appears to me at this stage; obviously I don't have access to DreamNow's thoughts.