Part of the series is about filling the hole where Helena Baxendale's Rachel used to be although a fair amount of the show will be about that loss and how even after many years such things endure. Seems wrong somehow not having her their but isn't that was death is? Either way, I had slightly hoped that they would have made the show as though she hadn't been killed off, that she would have been just in there just to mess with viewers. Having her long lost sister turn up wouldn't have been completely out of genre. Or have her Friends character Emily wander through. But no, she's not there.
Not that the creator Mike Bullen didn't try according to this Guardian set-visit:
"Following many years of being asked to bring the show back, Bullen finally agreed. The producers persuaded all of the original cast to return – with one notable exception. He did write a part for Baxendale, but she didn’t fancy playing a ghost. “She said, ‘Thanks but no thanks – it’s a crap part’,” laughs Bullen. “She definitely made the right decision. It was just me being sentimental.”"Well ... true, plus without heading off into proper fantasy she presumably also wouldn't have had her own autonomy as a character, simply hanging around, reacting to Adam. But the character is still there through her lack and because of that she's in nearly every scene.