Sunflower seed growing out of control?

My niece planted a sunflower seed in Pre- School and brought it home. Her mom my sister just had a baby so I'm helping them out a bit. We re potted the flower and water it everyday, and it's growing out of control! She's so proud of it, but between my brother-in law my sister and I none of us can keep a plant a live for very long. How should we care for it? It can't go in the backyard right now as it's all messed up as they are currently have someone landscaping it. There is a nice balcony that gets good sun when we have it, but it also gets winding up where they live, won't it snap in half we put it outside? Any help or advice would be very much appreciated.