FaceTime can be tricky to troubleshoot as it relies on multiple factors. Below I have included a couple articles that will assist you in troubleshooting this issue. In the first two articles, start with the sections labeled "Troubleshooting FaceTime for Mac/iOS". The third article I have included gets a little more advanced into troubleshooting the network which is most likely the issue.
Hope this helps,
Thanks, Jason -- we will try this. what is curious is that it worked well for a while (she is in the EasternCaribbean), then she came home on spring break, and when she went back it stopped working except when she uses her iPod (on the same network as her iMac) to call my iPhone (which is on the same network as my iPad) .....and it only works when she calls me. Very odd. that said ... . we will read the articles you sent and see if there is a nugget we can find to clear this up! thanks -- Tchotchke1623