If she wasn't the oldest, and if her siblings were similar to her in trying to have peaceful communication with the sailors, then I believe she would have left with John.

Well, it was more that she felt she was needed there because of all the Indians, not just her father.

I guess maybe If she had a sibling she considered both capable and willing to help make the situation run smoothly she might have gone, but I still don't really think she would be comfortable leaving her people at such a turbulent, uncertain time. It would be a lot of responsibility to lay on a sibling because you felt like going off with your boyfriend, especially when Pocahontas would always be more invested in the situation because of John.

^^I agree. You always say what I'm about to say lulz xP

agreed with @Mermaid-Tail.

I again agree with the above comments.

She was needed there she stopped the war if she left who knew what would happen

It all depends on what her sense of family obligation would have been with a sibling along for the ride.