A Spy in the House (and the rest of The Agency series) by YS LeeRead about another entry on the list.
Oh, how I [Gwenda] love this series! How about an alternate Victorian England where a secret women’s detective agency, with a girl’s school attached, natch, exists? Yes, right. So much yes. Main character Mary Quinn has secrets of her own and like most of my favorite sleuths has a knack for getting in over her head and then coming out on top anyway.
--Marshal Zeringue