Get a rubber band and place it on your wrist. Each and every time you have a desire to snoop, snap that band. Your focus will be on the sting. Also, set up a change jar and again, if you get the urge to snoop, drop some coins in the charge. I bet you will have it filled up in no time. We all go through a period of wanting to snoop...it's very normal, but there comes a time when you just have to back off and leave them to it. They are like teenagers and what do teens do? They constantly text, email or FB each other all of the time. Right now you are the authority figure (dad) and she's going to keep on doing it and who knows, she could be testing you to see if you will snoop or say something to her about it...but I would remain silent.
If you aren't sure about doing something, come here to post. Someone is always around. MGoBlue once said "when in doubt, do nothing". That is a choice and one that I have used many times and it's saved me from doing something really stupid.
The more you read, the more you'll begin to understand that what they are dealing w/and also how you can take care of yourself.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.