Photos Stale until plugin cache emptied

Hi –
This is a great plugin but I have one issue with it. My client will place a temporary placeholder image as the featured image of a post. Then, days or weeks later, they will replace it with a different image.

When we generate the RSS feed that includes that post, the link to the featured image is stale – it is of the placeholder image that was originally saved. Even if we clear the browser cache, this persists. However, I saw that there was an option in RSS Image Feed’s settings to clear cache, and when I did that the problem was fixed.

However, I cannot ask my non-technical client to go in a clear the cache each time she needs to send out a newsletter using the RSS feed. Is there a way to force the plugin cache to be refreshed or emptied, or not to be used?

Thanks so much for your help!
Cindy