Hi, do you mean she called you to say she was 5 weeks pregnant on the 11th of January? (If you are really talking about February, do you mean this happened last year?)
It can get confusing to hear a number like so-and-so weeks "pregnant." Doctors use a count for the pregnancy time period that begins on the first day of the woman's last period. By the way a doctor counts it, if a woman is 5 weeks "pregnant," she is only 3 weeks since conception, because on the first day of her last period she would not have gotten pregnant yet. But they do start the count there even so. If she told you she is 5 weeks along in the pregnancy time period on January 11 [given that I am correct in assuming you really mean January 11 where you wrote February 11 above], she would have conceived about three weeks before January 11, on about December 21.
When you say "round about the 7th of December she came to my house while on her period cause we were talking for a bit," is that a euphemism for "we had sex on December 7"? If so, is that the date that worries you? If she got the "5 weeks" number from her doctor, and didn't just invent it herself, you do not need to worry about the sex on December 7. (The doctor would not have meant she conceived 5 weeks earlier.) Also, you say she was having a period on December 7. A period means she was not already pregnant on December 7, and also that she was not ovulating on December 7. An egg comes down only once a month and lasts for one or two days. It doesn't come when she is shedding her endometrial lining (having a period).