I had no clue that my husband was an addict until we were married for over a year. I thought he was just crazy or something. He hid it from me very well because I am like you - never touched the stuff and I just trusted him.
He made a good chunk of money and yet we were just getting by. I figured out he was withdrawing large sums of cash and was always going "crazy" around my paydays.
I'm short so he hides his stuff up high. So now if I need to snoop I just get on a chair and look on top of everything.
She may be taking some stuff in front of you, her "prescription" and then popping more behind your back. Look where you wouldn't normally look - like a drawer filled with things you never use, a closet you hardly ever open, etc.