Help !! Please !!

Hey guys well my sister just found out she was pregnant she was actually 4 weeks the other day ! Well she went to the er to confirm the pregnancy they did confirm she was pregnant...... BUT..... didn’t see anything 🤦🏽‍♀️ the dr told her to wait and schedule with her obgyn , she will go on Wednesday next week.... anyone else had this problem but everything was fine ? Im trying to be encouraging so she wont stress but im clueless

UPDATE: NOT EVEN A SAC WAS VISIBLE