I'm going to lock up my edibles, so that my niece does not get high on them anymore.
How did it happen that she ended up getting high?
The dog got into the edibles and she saw it was eating them.
If your dog is getting into your edibles you need to take proper precautions to store them. Your niece may not understand the kind of effects edibles can have so you should try to talk to her about them.
It's important for people to know how to be accountable for your own actions. I hate that people point fingers across the room, trying to make excuses for their own mistakes. As far as I'm concerned, my niece is responsible for her own actions.
If you want people to be accountable for their actions then that should also apply to yourself. They're your edibles and storing them is your responsibility. If someone finds them that means you didn't do a good job of securing them.