which base awarded on this obstruction?

[shipwreck]

During a run down between second and third, the runner was obstructed by the shortstop (who at that time was out of the play). We signalled and verbally stated that it was obstuction. The fielders and runners went back and forth a few times, and the runner finally tried to make it to third but was tagged out. Here is my question. What criteria do you use to know where to place the runner? In this case she was obstructed halfway between second and third, and was going in the direction of second when she was obstructed. Do you put her there for that reason or since she tried to go to third but was tagged out do you put her there? I know the rule says you place her on the base she would have reached had there been no obstrution, but in this case how do you tell? Dave