Im baby sitting my 12 year old niece today and need some ideas on what to do today?

My sister asked me if I could watch my 12 year old niece today because she got called into work. I am her 40 year old uncle and do not have any children. Her and I are close but I don't have a clue what a 12 year old girl does for fun on a boring sunday. I know she went to the movies yesterday and baked cupcakes last night with her grandmother. Its a nice sunny day today in Baltimore with a high of 81 degrees. She loves arts and crafts, painting, outdoor activities as well but I haven't a clue. Can I please get some ideas or specific activities to make this a fun day for her. Are there any science kits or do it yourself projects that I may be able to purchase at walmart, radio shack etc..... Any ideas are highly appreciated. thanks