I don't think there have been any new BSC books for a couple of years. The last one I saw was about Mary Anne's house burning down and new beginnings and then Ann Martin wrote a few really odd books about the same characters (different series) in which some of them really disliked each other (like Stacey and Claudia--because of a boy). At the same time, the new Little Sister books started having disclaimers in front that kind of indicated they were being ghostwritten. Then they all disappeared.
I read online and in Ann Martin's bio that she has health problems due to a spleen removal but it also sounded like she was getting real weird about contact with the public.