Why would she be kidnapped and would this be a good idea?

I want to write a story about a girl who was kidnapped and is a long lost princess. I understand if it's like Shrek or Tangled but that's not what it'll be like, honest. I want her to be kidnapped for a reason but I don't know why she would be. Could you please help? And please don't say i need to create something that hasn't been used. I don't take peoples ideas. All I need is a reason why she would be kidnapped and maybe some names for her. Thanks