2 runners occupying the same base ...

[mcrowder]

It's been a while since I ran an ASA game, but isn't there part of the rule that tells you when LBR becomes in effect?

In the scenario described above, you can't stop play and call R1 out for standing on 2nd. I can't find the verbiage to interpret that rule that way. (Not to mention that R2 can certainly start heading toward third base).

You mention intent. The purpose (intent) of the rule is to get rid of the intentional stopping between bases to force defense to make a play. I don't believe it's intent was to penalize a runner for heading toward a base that's occupied, if her intent was not to force a play (her intent, in this case, seems to simply be a mistake - it's 10U after all).