had sex six days ago my ovulation cycle started on the 6th, pregnant ?

Of course she can buy pregnancy test, but it is of absolutely no use if it is taken too early, and only six days after sex is too early for home pregnancy test to detect pregnancy. It too early even for some types of blood pregnancy tests you have at the doctor's. So, yes, it seems like you do have a chance to be pregnant since you did have sex during your fertile days (about 3-4 days around your ovulation), but the quickest test you can take is at the doctor's - it should be able to detect pregnancy some 10 days after the sex. And if you decide on taking the home pregnancy test, you will have to wait at least for two weeks after sex, or for the day after your period is supposed to be.