I assumed this was a clear-cut double, but I asked a scorekeeper who has scored at a high level, and he indicated that the scorer can judge whether or not the batter would've reached second safely. If so, double. If not, an error on the first baseman for the obstruction.
Here is his answer, although keep in mind he thought I was talking about baseball. Don't think it would be different for softball, but it would depend on the rule book.
Like so many things, the answer is, it depends. And the answer for high school could be different than for "regular baseball". In high school, ALL obstruction calls have an award of at least one base. In real baseball, bases are awarded automatically for type A obstruction, but only if the outcome was affected for type b obstruction. (Type A is obstruction on a runner while being played on, or on a batter-runner before reaching 1B. Type B is obstruction of runner not being played on). High school doesn't have type A and type B, there is just obstruction.
Since high school automatically awards a base, the batter may be awarded 2B, even if the um[ire wasn't sure he would have made 2B anyway. So in high school, the scorer should judge: absent the obstruction, would the batter have reached 2B? If so, score the double and ignore the obstruction. But if not sure, score a single and a error on the first baseman for permitting the advance. In case of doubt, I would lean toward the double.