I have had a similar problem with a recent repair that I did. However, the replacement LCD assembly that I ordered worked properly. It may be a faulty part that y'all received. LCD assemblies are sensitive pieces of hardware when shipped alone without the mid-frame. Simply dropping a phone and not having signs of breakage can cause an LCD to not function.
Anyways.. I'm interested in hearing how this turns out for you. Hopefully the replacement part is the cause! You may consider reordering the replacement part with the frame already attached to the LCD assembly. That is predominately how I order my replacements as they are less likely to suffer any shock damage.
Oh! One tip for your friend. Check the cables that are at the top of the LCD without the glass on (of course) as they have a tendency to bunch-up and bend to extreme angles when removing the glass. It's an inevitable thing, but it is wise to inspect them. DO NOT PULL UP ON THE CABLES AS THEY ARE ATTACHED TO THE LCD/DIGITIZER/BACKLIGHT BACKING!