I've had early dating scans and for me, I have seen a heart beat as early as 6w 1d, and not until as late as 7w 5d (resulting in DS1!). I think it is pretty normal if all they can see is the gestational sac and the fetal pole, but no heartbeat. For my viability scans though, I was never sent any earlier than 8wks.
Fingers crossed for your friend. I hope all is well.