She knows you want share her, right? Why is she being secretive? Can you casually tell her you picked up her phone and you noticed she had a password installed? You could mention that you never noticed her having one before. You could straight up ask her if she didn't want you see anything after that? If you just want to let it happen then leave the phone alone and go back to being oblivious. If you don't want a surprise then you need to ask her what her plans are?