Ideas on what to write about

Forever & always

( thats the title of the book^)
Instead of harry being the only chosen one he had a twin sister her name was Taylor potter and she had the lightning shape scar on the back of her neck and she was quite pretty, red hair , green eyes, just like her mom and she went through the same things as harry and got into Gryffindor, but when she falls for her brothers enemy what happens?