Id had my "period" on time and normal, was a week late and took a test with a bfp, went to the dr and they did a hcg, the following week i went for a US being told we may not see much and the tech looked at me kinda puzzled and asked how far i thought i was and i said i was about 2weeks late, she then said "uhh your about 20weeks, let me get the dr" lol my levels had dropped and read about 5-6weeks by then
HcG levels rise rapidly in the first weeks then taper off around 10-12 weeks as the placenta takes over. Ultrasound is more accurate but the bigger the baby is the harder it is to date. however ic they saw a fully formed fetus and its pretty big i go with the ladies saying she could be in the middle of her pregnancy. She probably carries so she doesnt really show everyone is diffrent. sounds like she got some explaining to do.