Question [Q] Verizon certified like new to use in foreign GSM market?

First, I'm not sure if this is the right group to ask this, but here goes.

A couple years ago, I bought a used HTC Resound (I think) for a family member from overseas who had a really crappy blackberry. We installed her SIM and the phone worked fine, here and when she got back to the country she is living in--which is GSM. Anyway, after two years, that phone has been having trouble! So I picked up an eBay Verizon "certified like new" LG G2 replacement for her. This phone has never been activated. Do I need to activate it on verizon before I can give it to her? I had a French SIM that I installed to try setting it up, but the setup wizard said "unknown Sim" and would not let me go any further. So my question is, how can I prepare the phone so she can just swap the SIM from the resound to the G2 and it will work.

I also have a G2 on Verizon. Would installing my sim in this phone to set it up and then removing it work? Or would that tie my sim/verizon account to the new phone?