Personally, I wish they'd kept Rainie on the straight and narrow and just had someone else for Cora to anchor and interact with. I don't understand what happened to tip the boat again for Rainie. I also think it's a bit weird that she seems to revert to the same outfit whenever in the midst of an addiction storyline. Does she hide them away and return to change into them when she falls off the wagon? It's just a shame they don't utilise a mother-daughter dynamic when it's there - it would bring so much out of Cora. It's also not a relationship dynamic we see much of the on the square any more, save Carol and her daughters. I suppose there's Linda and Nancy, but once she's "got her in a dress" I'm sure that'll be it for them.
I don't know. On one hand it's realistic to show an addict lapsing back into using, but I think they just wheel on Bad-Rainie whenever they need someone to hiss at Ian Beale or be a right nasty bastard when Janine's not about. I think it's more about needing her to do that than progressing the character, which is a shame as she could have a place on the show again, for a bit.