I'm somewhat relieved to see I'm not the only one who made it to adulthood without reading Streatfeild (hadn't even heard of her until 2003).

Ballet Shoes is her best known, and the characters in that pop up in several other books, so I'd definitely start there (if a non-slemslempike person is allowed to suggest). The Chicklit classics book club read Streatfeild's The Painted Garden alongside The Secret Garden, which works very well.