Not okay! You wouldn't spank another adult who was misbehaving and treating kids with the respect of an adult immediately handles behavior issues making them take responsibility for their actions!
Cute post! I also love taking pictures of my kids and nieces and nephews but usually take them on my iPhone. I have also found incredible apps that help keep my photos organized and I share the photos on Instagram:)
Well it's different for everyone but one could definitely assume that by 7 to 8 years old she should be able to complete all of those behavioral tasks. She should definitely be able to chew with her mouth closed. Maybe having a conversation with her mother about these issues your niece has would...