In a similar vein to the author being of her era, listening to bits of The Secret Garden on audiobook recently was a very different experience to having had it as one of my favorite books as a child and young adult! I have a great deal of nostalgia for it and still love it for its strengths, but it's not as much of a pleasure to actually re-read as it once was.

I'm not as versed with A Little Princess (there was no gardening, after all), but I agree with you and can't imagine FHB casually failing to shine a spotlight on Becky's race if she'd intended for her to be other than white. On the other hand, books should always be willfully interpreted by the reader in whatever fashion they choose. ;)