@Cid I doublechecked her works on Bookmeter and it looks like I'm almost certainly wrong, but only because Gosick was republished through mainstream labels and outsold the light novel versions (not that Bookmeter is accurate to sales but when the first volume has 10000 readers from Kadokawa Bunko and 2000 from Fujima Mystery one can spot a trend.)
Red Girls is split over two editions but has ~9000 and A Small Charred Face at around ~4000 (both still far higher than the average light novel.)