What I don't like about the earlier Sybil bit is when Madge has been told (by Joey) that "Sybil is giving herself airs" she apparently looks at Sybil decides she doesn't like what she sees and tries to knock her down. I'm thinking of that bit in Highland Twins where she snubs Sybil when she says that Robin isn't a blood relation.
I think that Madge had much more depth in her to leave it like that, and would have realised that Sybil was actually very insecure in her position in the family. Yes, she would have pulled her up on remarks like the one above, but she would have also seen that she needed a bit of attention.
Think of it from Sybil's point of view who she is rivals with for attnetion.
David-the first born, very much in charge of "the babies"
Rix-also quite dominant and has Peggy looking up to him.
Peggy-delicate and needing attention
Primula-also delicate and needing attention
Then she gets a new baby sister, who jilts her out of her place as her family baby, plus the position of being her family's little girl.
She's very much the forgotten middle there. I can see David and Rix getting taken out for "manly activities", Peggy and Primula being fussed over at the mere hint of illness, the babies who naturally need more attention and Sybil there who is always well and doesn't need the help the younger ones need nor the extra energy to be run off that the older ones need.
But I never bought the idea that Daisy moved to Joey's to avoid Sybil, can't remember which book that's said in. Because at the stage she moved Sybil was very much a nursery child, and Daisy was a school chilc. I also couldn't see Daisy moving out to avoid her, but leaving Primula, who she's very protective until EBD forgets about her, stuck much more with Sybil than Daisy ever was.
Daisy might prefer to be with Robin, which is fair enough as they would be closer in age, but I suspect she would have wanted to stay with Primula however unhappy she was in a place.