I used to love her books, I think I read the illustrated mum, Vicky angel and the suitcase kid plus the second Tracy Beaker the most because those were the ones I owned. But I used to get the others out of the library and read those too. I didn't find the illustrated mum scary or traumatic at the time. I think because it has a happy ending - they all sort of do, don't they? I probably just naively thought everything would get better. It's with an adult viewpoint you can "see" into the future and guess what life is like going forward for the characters.
I mostly read them from about 11-16 and tended to see them from the point of view of showing you what it was like to have a different life experience. I think they did help me have empathy and see a different perspective. I also think they do a really good job of illustrating that even when parents aren't ideal in terms of providing stability, security, financially, routine etc that a lot of the time that doesn't mean that the parent and child don't love each other. In fact, that can often be very strong. I think that's the most important message I got from the books really, and this is sometimes picked up on too, directly by the characters, like when Dolphin goes into foster care, and the foster mother washes her black witch dress because she thinks it's dirty and ragged, but Dolphin is devastated because it fades the black and it smells like washing powder, not its "magic witchy spell". And I think JW is very good at observing and illustrating this kind of thing, where adult concerns override what is really important to children. There were parts of Tracey Beaker that touched on this kind of thing as well. I think it was always clear why the characters act "bratty" but maybe that was me being that much older when I read the books to realise that.
The only one that really upset me was the Diamond girls, I remember being really shocked and upset by the force feeding scene, and I'd forgotten the nail cutting but yes, that as well. I found that one really really hard to read specifically because of the scenes with that neighbour.
Tracy Beaker the TV series was nothing like the books. But I think you couldn't really do a TV series about a children's home like in the book version of Tracey Beaker and have it be actually suitable for children. There are bits in the books where she just alludes to things where as an adult you fill in the blanks, but children wouldn't, and you couldn't show that on TV. I have no idea how realistic JW's portrayal of being in care is, but I suspect it's a bit out of date compared to when the books were released and certainly in comparison to today.