I don't see Whitney's feelings for Mick as anything resembling the Molly and Kevin affair, and I certainly don't think she's a witch.
I've still got a lot of sympathy for Whitney. The girl is obviously very, very confused and the two lots of sexual abuse she's suffered have understandably messed her up in a big way. Harrowing experiences like that often affect a person profoundly for the rest of their lives, especially without professional help. She's unhappy and lonely due to Lee's depression, and has obviously grown to see Mick as someone warm and loving, who takes care of his loved ones, and who makes her feel safe. I think her developing feelings for him is entirely understandable given her history. She also may be confusing his attention as romantic feelings because that's how Tony manipulated her into a sexual relationship.
Acting on her feelings is, of course, totally out of order, but I agree with maidmarian that her boundaries are going to be skewed after being abused by two older men she trusted implicitly. Hopefully Mick will put her straight sensitively.
I'm positive this won't develop into an affair given what Danny Dyer has said in interviews. I also haven't read anything about Whitney leaving.