Is AUTHOR wrong in the post ? POST : So my birthday was a few days ago and I recieved a number of birthday cards, 2 of which were fairly personal from my SO and my sister. When I returned from school my mother referenced an inside joke I has with my sister that there was no way she would have known about, when I questioned her she admitted to reading my sisters letter but also said it's not like I was going and reading you're girlfriends letter. Now this was where I said that that violated my privacy and asked that she not do so and she became defensive and said I'll never enter enter you room again, and that she csnt believe that I'd be mad over something so small. 

So reddit AITA?

mobile formatting sorry.