First you'll need to know what kind of herpes your girlfriend has. Did she, for example, contract genital herpes or herpes on her lips (mouth)? Genital herpes is caused by Herpes Simplex Virus type 2 (HSV-2) and is a sexually transmitted disease. Herpes on the moth, skin, eyes or in the oral cavity is caused by the Herpes Simplex Virus type 1 (HSV-1) and it is transmitted via direct contact (kissing or drinking after an infected people). Both types of infections manifest with skin/mucosal lesions. Initially, HSV infections affect the local sensitive nerves and stay hidden in the nearest sensitive ganglion. When the immune system becomes weak, the hidden virus causes skin/mucosa lesion that cycle in 4 stadiums: erythema, vesicula, ulceration and crust with healing. There could be itching and pain present, or the lesions can manifest swollen and painful local lymph nodes. Given your symptoms (sore throat), it seems that you still have not yet manifested an HSV-infection.