If the girl is considering carrying the pregnancy to term, then absolute top priority is getting the chlamydia treated. Untreated chlamydia can cause serious problems during pregnancy, including premature delivery and blindness or pneumonia in the baby.
Prenatal genetic testing can be done using a sample acquired through amniocentesis or CVS (chorionic villi sampling). However, these procedures have risks for both the woman and the fetus, so most doctors won't do them just for purposes of paternity testing. There is also apparently now a method of non-invasive testing based on fetal cells in the woman's circulation.
As far as I can find out from the net, these tests can usually be performed between the 10-12th and the 20th weeks of pregnancy, but you'd need to consult a doctor to get reliable information. And they can cost up to several hundred to one thousand dollars.
I don't know if Planned Parenthood offers prenatal paternity testing (they may not, since it's not a medically-necessary or health-related procedure), but you can find out by contacting them: Planned Parenthood (1-800-230-PLAN).
It's also important for your friend, the girl and her boyfriend to think about why they want the testing done, and how the results will affect them and their choices. If the girl wants to carry the pregnancy to term anyway, then paternity testing can be done more easily and cheaply after birth. And simply finding out which guy is the biological father isn't necessarily going to be the best way of determining which (if either) she wants to raise a kid with, or if she wants to have a kid at all.