She made a dna bank of him to do her uni bio essays on and use his dna as guinea pig. Dna screening (detection of genes carrying diseases), dna fingerprinting etc, She checked hers and then she did his dna too, to check compatibility and see if there's possibility of diseases, gene screening. Like the tests they run in vitro fertilisation clinics for down syndrome, thalassemia and other congenital disease on embryos, she can infer directly from the progenitors without testing the embryo. This was probably jokingly suggested by her teacher and I think she's not the only girl doing this in her class.

She has many readily-available unused emergency condoms. Their purpose is not redundancy. The dna bank project is an ongoing life-long hobby, and there will me more.