Writing about the same world but from a different angle

I've started work on my new novel which inhabits the same world, albeit at a slightly different time, as my last, Kindred Spirit.

This time I'm writing in third person because I think it'll suit the plot arc better - it'll give me more distance and time, as I anticipate this story will need a slower, more contemplative feel. My central character is completely different to Annie in Kindred Spirit - she might be female, at a similar point in her life, of a similar socioeconomic background, but she's quieter, more insular, at times a little sullen. Oh, and she suffers from epilepsy, too, so the research to get that right is underway.

This character had a minor role in Kindred Spirit, and I don't think we got to know her too well because she's more introverted than her compatriots (true to life, hey?) so I'm enjoying exploring her more. So far, so good.

But what I'm worrying about - before even getting to that point in the story, of course - is when she meets one of the more dynamic characters we already know from KS. Though they will be in a different country, a different climate, a completely different scenario, a similar pattern will emerge as in KS - after all this is Kim's story about her involvement with Chantrea. And I'm concerned that for a reader who has already digested KS, this will seem predictable, too similar.

I suppose the key is to ensure that Kim's voice remains different: that she never reverts to Annie's psychobabble but continues to calmly, almost cynically, weigh up the characters and the settings around her, even in third person, so it feels unique and gripping. After all, plenty of stories have the same action - so many YA stories encounter pregnancy, parental divorce, drugs, bullying, paranormal events, etc - but it's just the characters who tell them and the environs that carry them which make all the difference. Wish me luck!