If shes not testing the trigger out, I would wait at least 12 days after the trigger shot. It can stay in your body up to 10 days. I started testing earlier but was not sure whether the lines I got were from trigger shot or being pregnant. In the end it turned out I was pregnant, but if I was to do it again I think I would try to test out the trigger shot or wait. Of course easier said than done!
Good luck to your friend!!
Xx