Ok, her is a little bit of a physiology lesson:

Most women have a 28 day cycle. The start of that cycle begins with the mestrual perion which lasts 1-5 days. Day 6-12 the endometrium begins to repair itself. Day 13-14 is the ovulatory period. Then, days 15-28, the uterus prepares itself for fertilization, if this does not occur, on the 28th day the process starts over.

This means that your women has only a 48 hour period in a whole month in which she can get pregant. You said her period ended on Thursday and this occurance happened on Saturday; I would say she is NOT pregnant. Don't sweat it.

I would let my big head start doing the thinking!