Do you think a 11 son to be a 12 year old should be able to stay home by her self?

Okay so me and some of my friend where going to go to the movies and hang out today. but instead i get to stay home and babysit my little sister. so far this summer i had to babysit her about 15 times when my other sisters and my parents are not here. it seems like every time i have plans i have to stay behind to watcher when she if 12. do you think i should have to spend all my free time watching her or should she be able to say home by her self?