No man's girl - BuckyBarnesxReader

This is a story about Y/N that is Steve Roger's little sister.
Yes, Y/n's brother is the fantastic hero who got the serum and got stronger, but what if I told you that he wasn't alone.
Y/n got the same choice as her brother, which she took without thinking twice about it. But there is a twist. Y/n didn't get the same serum as Steve, which they didn't tell her before it was too late.
Y/n had gotten superpowers.
She was now a super-soldier with powers. But what kind of powers does she have? Okay, listen closely. Y/n has the ability to control the four elements, fire, earth, water, and air. She loved them at first but got scared of them after a few days. She Was afraid she would harm anyone she loved, so she stopped using them.
She loves her brother with all her heart, but there is one part of her heart that is meant for someone else, but can they ever be together, or will her brother tear them apart.
Will she get her happy ending with the boy she has loved since the '40s, or will she end up heartbroken and be no man's girl?

TW: Self-hate, suicide, smut, and so on. This is a warning, so please don't read it if you aren't comfortable with stuff like this.