A mischievous blonde with a questionable hairstyle joins a well-established and beloved series, moves into the family home, and...hmmm, this is starting to feel very familiar. Yes, the Cousin Oliver alarm went off for many public-television watchers last week when, in the season finale of Downton Abbey, we found out Cousin Rose MacClare (Lily James, right), with all of her dancing, rebelling, and mother-hating melodrama, would be moving in with the Crawleys next season. ''Cousin Rose can be pretty irritating,'' admits James. ''I hope with the new [season] you see more of who she is and why she's behaving like that. She's just sensitive. And how can you survive with a dad called Shrimpy?'' Though she won't divulge any details about season 4, she's hoping people warm to Rose. ''I'm still really new to all of this,'' James says, ''but I'm going to try to focus on the acting and playing it for the truth. Even if it's an annoying truth.''