How much of the script have you written? If you haven't already you should write what you've already decided on. Then once you get a feel for the way the story is playing out, you may come up with something else.
The other thing I do when I need ideas is I engage myself in a mindless task. For example, washing dishes or mowing the lawn. I happen to be a massage therapist so I find that a great time for thinking, too. Basically do something where you're using your hands but you don't have to think too hard about what you're doing. Then just let your mind wander. Think think think think think.
The important thing with this is to make choices. Start going through your 'What Ifs.'
What if the girl is mute and this is her only way of communicating?
What if the girl is kidnapped and is only let out to go to the library and this is her attempt at seeking help?
You get the idea. Then when something seems ok, it doesn't even have to be great, start running with that. Just pick something and do some more 'What Ifs.' Trust me, pretty soon you'll have an idea. Resist the urge to write everything down. Keep doing your mindless task, the busywork for your hands, until you absolutely are burning to write down your story. Then do it. In script form.
Bye bye, so-called 'writer's block.'
Just my two cents. May or may not work for you. But it's something to try.
And I'm planning to make it a ROM-COM (romantic comedy). 
