OMG what wonderful news.
This happened to a friend of mine at Xmas, scan at 7wks no HB. She went back 5 days later for a d&c the doc scanned her again, there was a little bean wiv a lovely HB and that little bean is now 8 wks old and she is adorable.
Millions of happy vibes to your sister, and cant w8 to see pics of her new summer baby to be.
V x x