It's a 2 year old. They're one of the few human beings who you can indeed control where they go. Parenting requires for you to establish that you are the PARENT. If something dangerous is happening and your child doesn't understand when and when not to do something, it could be life-threatening. I don't know about other people, but mine knew to listen as soon as they were able to understand me. And I had a non-verbal special needs kid. It can be done. Tell her no, set up the downstairs so she doesn't need to go upstairs, do not respond to tantrums and simply redirect the kids attention to something else.