Yggdrasil has the capability to bug the garage, but it's unlikely that they did so previously and as long as Michi is outwardly compliant I don't think Takatora would order it to be done without her knowledge.

I can just see Ryouma saying something like "Minato is physically trained! Your sister provides invaluable data on the average young woman-- not that I'm saying Miss Kureshima is anything less than extraordinary, of course."