I'm having trouble understanding what the problem is. This is an EX employee who is bugging her former company? Fine; she calls and says "I got the check instead of it being sent directly to Great West". Assuming the check is made out to Great West, the answer from the former employer is (and only once):
"Oops! Sorry. They sent it to you by mistake, so now you should send it to Great West. Nothing we can do about it but it's not a tax problem because the check is made out to Great West and will be reported as a rollover. Have a nice life!"
If she calls again berating the HR department; the answer this time is:
"Still sorry; we told you what to do. Do it or not, but now it's in your hands to make it happen. Don't call again."