If you have nothing to hide, I wouldn't change the passwords. One time, she was rummaging around my computer and I came home to delete a letter that I wrote, which she had already seen. She said, go ahead, change your password, lock me out of your life. I said, I am not going to do that.
Then, when I found out about OM, she changed her passwords, but I didn't change mine. Later, she was reading some e-mails of mine and found some info that she didn't like about OM (He found another woman to have sex with). I found out she read them and asked her about it. She said, yeah, I read them, but there was nothing interesting in them anyway and I won't be reading them anymore. I told her that she could read them anytime she wanted, because I have nothing to hide.
On the other hand, if you have separated your financials, I would make sure that those types of passwords are secure.
Just think about what it is that you don't care if she knows and what you don't want her to know.
