If she's responding to benedryll-- then it is something environmental from the new addition, or a food allergy...
OR the benedryll relaxed her enough to reduce the stress...
BUT: there are MANY stories of people getting VERY ill from respritory problems after remodeling their homes.
Carpet fibers and backing dust, Mold released when tearing out old carpet/walls/windows... I'd go to Lowe's ASAP and get a "whole-house" air cleaner-- they aren't cheap-- around $120-- but if it makes ALL of you better-- it is well worth it, and a LOT less than medical bills for both Kitty AND the family!!!