Hi Cheryl and welcome
good to see you were able to post your question up. The answer is yes, the 10km program is primarily good enough to convert to racing a 21km and in the past athletes have raced successfully over the distance using the same program structure with the major change being the 1st weekend Sunday long run.
so we can convert the pace for the 10km program and then make a few other changes, you should look at the sub 40 minute 10km program
and then with your feedback we can tailor it to suit your needs
Hope this helps