Gladys is in
Explanation:
MATS not MAC 1,2 MA PATSY not PACY 3,4 TS SETS not SEC 2,4 ES TSONGA not CONGA 1,6 TA MISC not MIST MISTS 1,2 MI CARS not TSARS 1,3 CR DOC not DOTS 2 O DITSY not DICY 1,2,DIS PITS not PIC 3 T ARC not ARTS 2 R SIC not SITS 2,3 IC ITSY not ICY 2 T
where
each "X not Y" is a word meaning X in which we can replace C with TS or vice versa to get a word meaning Y; we then extract letters at the given positions.
Credit where due:
Jay and Omega Krypton solved some of the clues before I did, though as it happens I didn't look at their answers.
