You can throw up for 100 different reasons, and breast tenderness happens for another dozen. Generally it's due to hormonal changes. Symptoms mean jack, and just because you're sick or might have breast tenderness doesn't signify pregnancy. I doubt she's pregnant.
Then unless she Ovulates 5 days after her period, then no, she can not be pregnant. The stress of her thinking that she is pregnant can be causing her symptoms. Minds can play tricks on us. Also, if there a chance that she could have caught a stomach bug? I don't think that she pregnant, but if she has not gotten her next period, then have her take a test
Did you all unprotected sex at all after that time and after her period?
Because she has been throwing up and her breast hurt?
Why does she think she's pregnant? Generally speaking ovulation occurs two weeks before a female's menstrual cycle (though this isn't set in stone) and you also don't experience a period during pregnancy. This is just due to the nature of both. You can bleed while pregnant, but it's not a true menstrual cycle. If she's concerned, have her take a pregnancy test. It will show an accurate result at this point.