"The Secret Garden" is much better in that its female protagonist, Mary Lennox, isn't as perfect as Sara, but even that book has its problematic aspects. Mary disappears towards the end of the story and it becomes all about Colin, and I totally understand why so many disability advocates would have issues with "The Secret Garden." One, we're only given very generalized aspects as to what afflictions Colin suffers from and of course, the magical cure through positive thinking. Given that most people with disabilities will never be magically cured, yeah, you totally understand why stories with those would rub them the wrong way.
*********SPOILER ALERT!!!******
I would interpret it that Colin was never disabled but that the doctor was trying to kill him in order to inherit Misselthwaite Manor.
Colin was born a little prematurely due to the accident that killed his mother, i.e. she went into premature labour then died (probably only 1 month premature, i.e. had a chance of surviving without medical intervention). He was born small and sickly and not expected to survive. I forget the exact relationship between the doctor and Colin's father Mr Craven, but it's mentioned in the book that the doctor was going to inherit Mr Craven's estate if Mr Craven had no heir. His wife died and the baby was probably not going to survive very long, therefore the doctor was all set to inherit it. But then Colin didn't die as expected. The doctor convinced Mr Craven that Colin was going to grow up to be sickly and a hunchback like his father and was unlikely to survive childhood. Colin spends his babyhood and childhood in weird contraptions that are supposed to keep his legs and back straight - but this was due to the doctor saying that Colin was
going to be disabled, not in response to any actual disability that he had.
When Mary first finds Colin, she can't see anything wrong with him - yep, she's not a doctor, but if the kid really did have a twisted spine or was growing up to be a hunchback, that would be noticeable. Mary specifically tells Colin that his back is perfectly straight. If he had problems with his legs that necessitated the doctor putting leg braces on him - there was no sign of that either. The whole thing about Colin having an unspecified medical problem - that suggests the whole thing was invented by the doctor.
Of course, when Colin finally does get out of bed, he can't walk. No-one who's been forced to spend their entire life in bed is able to walk. Through the help of Dickon, Mary, Ben Weatherstaff and the magic of nature, Colin learns to walk and becomes strong in spite of the doctor's attempts to make him into a permanent invalid and die young (essentially, a very slow murder) - it's not positive thinking that does this, it's because he was never disabled beyond the inevitable muscle wasting due to having spent so long in bed in contraptions that stopped him moving. The kids do all this in secret as they all believe that Colin can't get well while the doctor is around, and the doctor is very dubious about the idea of Colin going out to play, saying that he'll catch a cold and probably die. Colin gets his way because he's still the master's son and the doctor is an employee, but it's very clear the doctor doesn't approve and tries to discourage Colin from going out.
When Mr Craven finally comes home to find that Colin can walk just as well as any other kid his age, this is also the first time the doctor sees him being healthy and active, and rather than being delighted as one would expect from a doctor who has his patient's best interests at heart, the doctor is horrified and gets ready to leave. The doctor knows Colin's got a very good chance of living to be heir to Misselthwaite Manor and the doctor probably doesn't want to be asked too many questions about Colin's "illness" and miraculous recovery.
Maybe I just have a knack for interpreting books in really dark ways....?