Dianna Wynne Jones' _Conrad's Fate_ is pretty basic Jones--emotional abuse (including neglect) and the pain it causes, weird time/space events, sharp characterization, pleasant prose, and a happy ending that gets the reality-based characters away from those who are absolutely committed to not knowing what they're doing.
It's better than _The Merlin Conspiracy_ (two high-angst viewpoint charcters that, imho, weren't different enough from each other) or _Hexwood_ (I know there are people who love it, but I couldn't get into it), but not as wildly inventive as _Archer's Goon_ or as intense as _Fire and Hemlock_.
In any case, it's very vivid about the soul-killing pointlessness of being stuck as a servant in a noble house. The physical conditions aren't great, but they aren't awful--the emphasis is on what it's like to spend most of your time, and if you aren't lucky, your whole working life, repetitively smoothing the path of people who you're supposed to make sure don't notice you.
Jones gets points for emphasising that those upper class people aren't awful--they're just ordinary and oblivious.
There's a moment of genuine horror
( when )Odds and ends: This is a Crestomanci novel. For a change, the mother is neglectful and the father is vicious. The only other "being a servant sucks" fantasy novel I can think of is _The Ill-Made Mute_ by Cecilia Dart-Thornton.