Answer: Me
Step-by-step explanation:
Mine: you use mine when you are describing mine thing that belong to you, thus, it would not fix I need that statement.
I: I just by looking at it you can see it would not be grammatically correct, you use ‘I’ when stating ‘ my sister and I’.
Me: I sent the right answer.
Myself: is too formal for this sentence.
Hope this helps! :)