Maybe she spent it because she was pissed that you had a secret stash. I mean how would you feel if she had one? I have only heard of people having a secret stash for two reasons. Men it's usually because they need funds to do things on the down low from the wife. Women it's because they are saving up funds before they tell their hubby they want a divorce.
Not saying that is your case I just know shady people that have saved for those reasons.