Runner safe at 2B, but out for taking her foot off the base. How is that scored?

[blwanta]

How would I score this... I have a runner on first and the batter bunts (attempts to sacrifice) and the catcher picks it up and immediately throws it to the second baseman where the runner is safe (standing), but her momentum put her over the base and it allowed her to take her foot off the base and the second baseman had her glove still on the runner and was called out by the tag. How would I rule the play? I initially the charged the batter as reaching first on a fielder choice and the runner is out 2-4. Would this be correct?