The day after harrys 11th birthday

What if Harry Potter had an older sister by 5 year but the night that there parents died she was not sent to Harry's mean uncles house but to some were Harry will find her one day maybe they will meet the day he goes to Diagon Allie (hope is spelt that right)

P.s. I do not own Harry Potter characters just the once I make up.

Also I am sorry about the spelling mistakes I have dyslexia so I find it hard but oh well.