If "runs to second and is out by approx 4 feet" then 1st base, unless the judgment is that the OBS cost her 4 feet of running time.
The "stops, then takes a step back toward first and then runs" looks like she might have had time to beat the 4 feet on a continuous non-OBS run; especially if she was actually rounding and not just overrunning.
Probably not the case, especially with "she would have never gotten to 2B".
JUDGMENT, JUDGMENT, JUDGMENT.
Agree, an OBS at a base affects continuation, so protection after the base is correct.
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Is there any book in the soup that would be different?