Gruschenka

Gruschenka is more rude than a scoundrel; but I have mixed emotions. She was very rude when she refused to kiss Katya's hand and rubbed the fact that Dmitry loved her more in Katya's face. But if she was a scoundrel depends on how Gruschenka really feels about Dmitry. I also think it matters if she had made promises to Katya or not; that changes where her morals stand.
On page 150 and 151 Katya and Gruschenka are talking about Dmitry. When Katya says, "But now it will be you who save him. You gave your word. " Gruschenka replies, "Ah, no, I never gave you my word. It's you who were saying all that, but I didn't give my word." If that's true, then Katya made her own hopes high, that isn't Gruschenka being a bad person.
"...whatever I want, I will do...what if I like [Dmitry] again all of a sudden because I did like him once very much, I liked him for almost a whole hour. so, maybe I'll go now and tell him to stay with me starting today..." (151). If Gruschenka loves Dmitry then she does have the right to be with him. If she doesn't then she just likes to see others suffer.
Gruschenka definitely has attitude and doesn't let anyone push her around. She made a fool out of Katya when she refused to kiss her hand and brought up Katya's shameful past. This was rude, but it was true; Katya did in a way sell her beauty to Dmitry. I don't think that makes her a scoundrel, just mean.