Talk to Gynecologist on Pregnancy

My sister in law had last time her periods on 7th of september. Her cycle is usually 28 days but for last two cycles this was 30 to 31 days long. She had intercourse with husband from 14 to 21 of septmeber on alternative days. Then on 2nd october she has observed sone mild spotting and on 3rd october she did TVS to rule out any issue. That was conpletely normal. So she on the same day decided to go for beta serum hcg test and turned out positive although she had two days left in periods to come. Means it was eraly before her periods due date. Now on 24 of october she had her scan showing 10.3 mm gestational sac with no yolk etc and it showed that it is 4 weeks just. I kust want to ask that is everything alright could it be normal?