She must have been popular enough if she wrote 66 novels with the same lead character ... one a year for about 60 years ... and there was a British television / PBS series based on the books starring Diana Rigg from the late 1990s ... so, some lingering interest and clearly some during the author's lifetime (Ms Mitchell died in 1983).
There's a nice summary, btw, of "golden age" mystery writers at this page:
http://www.sldirectory.com/libsf/boo...y/classic.html