I got an assignment from my teacher that tells me to continue a story that he started. The limit is 1 page. The scenario is that Rose (the main character) is looking for a missing painting, inside someone's house. (They stopped at the point where she opened it) I don't really know how to write/continue the short story. Where should I begin? I don't have a lot of ideas and I brainstormed a little bit but I couldn't think of anything.
We cannot tell you what to write or help you brainstorming - that's your task as a writer. However, we can try to assist you with how to brainstorm.
It is very helpful, looking at a situation, to ask questions. How does your character feel in the situation? What is she thinking about? Why is she there? Going forward, what does she find? Etc.
The question I find most useful when I'm stuck is what would make the most trouble for my character? Stories strive on tension. You want tension, you need trouble. Keeping in mind who your character is, what her goal is, and what kind of story you want to tell (horror, humour, etc.), what would cause the most trouble?
Then, of course, you would need to resolve whatever trouble you've landed your character into. Or not resolve it - she might succumb to whatever. Either way, you'd need to wrap up whatever is happening.