I think she has changed some of the language for an international audience in the later books - whether her choice or an editor's - I noticed things like in the earlier books Adrian had "a nintendo" and in later ones it's "a gaming console" - sometimes it's because she's trying to be vague about the timeline, but sometimes it's more of a generic term rather than what a British person would call something. Lots of stroller instead of pram etc.
WRT timelines as well - Lucy's story Will You Love Me definitely has some embellishment as it's meant to have happened in the early 90s, but the mum was getting text messages at one point! She was skint and couldn't afford nappies or formula, how on earth would she have a mobile phone??
I like Casey Watson but do feel a bit like these are the exact same books dressed up for a middle class/lefty audience (Cathy) and working class/slightly more conservative (Casey) audience. The foster children are the same but the carer's own children have MC / WC names, even the adopted one (Adrian, Paula, Lucy vs Keiron, Riley and Tyler). Cathy being divorced from her wet ex-husband who works in an office, and Casey having a strong male role model husband working in a factory who plays football. Casey is set in the North as well whereas Cathy is somewhere Midlands or South as far as I can tell. Not London or rural. I bought a couple of the Rosie Lewis ones and they aren't the same - they are more like proper novels, I couldn't get on with the daft romance with the social worker, and the characters are more nuanced. However she references a lot of real world things which send me on an interesting google rabbithole.
Cathy and Casey are extremely easy to read and don't require any concentration, they read like Take A Break articles. I went and bought all the new ones in preparation for night weaning and I can't focus on the Rosie Lewis one when I'm half asleep so it's no use. But Cathy/Casey are perfect. I just re-read all the old ones when I run out because you can never remember the storylines anyway.
It's basically Jacqueline Wilson for grown ups. I used to love her books!