I think these couple of episodes were the episodes that defined Morag and the potential she had. Up until the wedding she had been judgemental and bitchy, yes. But once she got Roo back to her mansion, she became truly conniving, devious and ruthless - giving us and the writers a taste of how much they could do with this character. I think the phonecall with Celia and her pretend conversation in earshot of Roo was the turning point. I think the writers realised this and had already decided they'd have to bring her back, hence the closing shot of Morag watching tearfully as Celia took Roo away, which very much left her character without closure. (I could be wrong but I'm assuming this was the end of Morag's first stint).
Thinking back over the years, especially the early years, I realise I have often found the Stewart/Fisher family more interesting than the Fletcher/Ross, so I'm really enjoying these episodes and what's soon to come.