First you need to find a place you can have the party that she would never think of. Your boyfriend's house is good if she visits there on occasion. If it would be odd for you to invite her over to your boyfriend's house then that is not a good spot. When I had a party for my girl I had a friend that lived in a condo and he had access to the club house. I told my girl I was thinking about getting a condo and asked her to check the place out with me. The manager said to meet him in the clubhouse. Surprise! Worked like a charm.
Decorate the place any way you want, invite her friends to show up like an hour early. We had people park in the church parking lot across from the club house so my girl didn't even think of looking at cars that she might recognize.
We had a cake that looked like a watermelon, my girl loved watermelon. We also had watermelon on ice for after the cake. My best friend made the watermelon looking cake but stores are getting pretty good at decorating cakes different ways. From what you said about her maybe you can get a cake that looks like a book titled, "Famous 17th Birthday Parties" or " Name's 17th Birthday Party Cake". For entertainment maybe you can arrange to show your sister's favorite movie via DVD. And of course give everyone enough time to get invitations so they can shop for gifts.
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