My point was that I guess it could happen but that is incredibly rare. Ask to meet up with her.
My mom had intrauterine growth retardation with my little sister. Her body stopped supplying food to the baby. And they kept pushing her due date back. If my mom had gone by the doctors she would have been pregnant for an entire year BC my sister was so small. She was born a month late by being induced and she was only 4lbs 6 oz.
Everyone is different during pregnancy.My friend at work barely looked pregnant until moth 6 or 7. She could be lying but I don't know why you would want to lie about something like that. If she did miscarry maybe she hasn't fully come to terms with it yet and I can understand that. Your sister will just have to wait it out and hope that her friend is telling the truth and maybe her family has always had small tummies while pregnant. Sorry I can't be of more help.
Either the friend has a mental pregnancy and is actually 3months pregnant