Nope. She may not get it, but there is probably nothing you can do to prevent it if she does have it. Taking acyclovir may help reduce the virus so that the immune system can overpower it, but to my knowledge there are no cases of this happening in medical literature. And you need a doc to prescribe acyclovir anyway.
According to the Herpes Handbook at www.westoverheights.com, a woman has an 8-10% annual chance of contracting herpes in a monogamous relationship. That means even if a couple are not using protection and the man has herpes, there is only an 8-10% chance that the woman will get it over the course of a year. (this, of course, assumes that they avoid sex during outbreaks).
However, herpes is still spread even when people avoid sex during outbreaks, and women are more susceptible. If your friend is still worried after 4 months, reccommend that she take the herpes type specific blood test. If she has symptoms before then (itching, bruning, red spots on vulva, blisters in genital region, sores on vulva, painful peeing), send her to the doctor's to get tested.
I wish her and you the best of luck.
A one time encounter when the infected partner doesn't have any obvious genital symptoms is very low risk.
No, there is nothing your friend can do at this point but wait it all out.
By the way, symptoms for herpes are most likely to appear within 2 days to 3 weeks after the encounter (although they can sometimes crop up long after...). I realize these are going to be very stressful weeks for her x___x