She could very well be doing drugs. Drug addicts will carry extra clothing so that the smell is not on them, taking showers often also helps get rid of the smell. Drug addicts will hide things from their loved ones for shame of doing the drug and for fear of being caught and turned in. If she was really putting on makeup, she wouldn't be doing it in the closet, but she could have been doing drugs in there so she wouldn't be caught. She also could be hiding phone calls from her dealer. Taking calls away from everyone else, hiding her phone from you, and getting overly defensive over her privacy could all be seen as signs of having a drug dealer; not necessarily a sign of cheating.