Don't tell her you're keeping a diary. If she doesn't know it exists, she won't go looking for it. And don't keep buying those blank books with locks on them that obviously LOOK like diaries; that's just asking for the lock to be broken and the contents read.
Use a plain notebook that looks like one of your school books. Does she go through your school notebooks and read your class notes? If not, then just keep your diary with your school books -- you could even just keep it in your locker at school and carry it back and forth with you in your book bag.
Otherwise, you'll have to find someplace to hide it, maybe under your mattress or something.
You had to be able to post this question in private somehow. I personally have a private Tumblr. Make an account and your "main blog" has to be public but the second one can be password protected.
Just be careful to log out of Tumblr every time and you should be fine. She can't crack a password with a hammer. Thinking of passwords don't make it anything she could ever guess.
But don't make it something that you would have to write down either. Just make it a really long string of words or something like Ilikecookiesandbagelsnotwaffles . That way if you never write it down she can't find it.
Just double check your settings and make sure it doesn't automatically save your password.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.