well, basically her parents went through your typical whirlwind romance where one ends up moving to another country for the other and then end up with a kid, only to realize they weren't good together, even though over the course of at least a decade, they tried every now and again. her dad was in the royal navy and as a result, not around often and at one point, sort of decided not to be involved, which he regretted big time, so a half sibling could come along if, in that mean time, either one of her parents had a kid with someone else. the rest of those details, as far as figuring out ages, when, time frame, if it would even work, are up in the air. for a step sibling, i figured it could be a case of second marriages where both sides already had kids, although her parents never married, and could either be something where the kids are already older or back in the day after her parents finally decided to call it quits for good