10-11 weeks pregnant.. no baby on ultrasound?

Nicole • Mummy of 3💙💙💗 #4 due October💗

Posting for a family member. Based of last period she is 10weeks 1 day, based of the one time she had sex to conceive she’s 11 weeks 2 days. That’s what the calculators online say. 🤷🏽‍♀️ She had an abdominal ultrasound today and a baby couldn’t be seen. Just a sac. They said it could mean an ectopic pregnancy or that she’s earlier on than what she thought. However the father isn’t someone she has slept with regularly and knows exactly when she must have conceived, which she said was feb 6th, so she’s no earlier. And she also hasn’t had any kind of pain or bleeding to indicate a miscarriage or ectopic. Just a little bit of pink spotting that only lasted a day a couple weeks ago which I know can be normal. So what could be going on? I know it’s unlikely but Is it possible that it’s too early for the baby to be seen on an abdominal ultrasound? Or is there most likely something wrong? Anyone had any experiences like this & what was the outcome? Anyone have any idea how far along she could actually be based on her date of conception?