The whispering, or sub vocalizing is actually a good strategy to help her "remember". My daughter does this too and actually gets to take her tests in the hall so that she doesn't bother anyone. I don't think this is OCD at all - but a healthy, mature response to a problem. Post-its are another useful strategy - good idea showing her how they help.
I agree - it may be that her hard drive is full. Keep in mind that low working memory is very different than low cognition. If her VCI and PRI are strong, these are the two scores that are most indicative of "thinking ability". Working memory though, can cause problems with efficiency and work output. So, you will want to be sure she learns the strategies to help free up hard drive space and reduce anxiety and frustration.
