Questions: Had he ever let her use the computer before? Did he ever rescind any permission he gave her? There are other things that come in to play with this. But hat is not my primary point. I am not necessarily arguing that but it is not clear cut that she committed a crime.
OP though is an immature selfish jerk. He is "engaged" and is supposed to be a partner to his spouse. He wants to hide his assets and debts from her because ...
Quite frankly, he shouldn't get married until he can grow up and learn what being in a marriage means... Finances are a huge portion of a marriage -- how people handle money, their priorities, so on and so forth. if he can't have an honest truthful discussion with the person he says he wants to marry then he isn't ready for marriage.