Vulvovaginal Candidiasis: This is the most likely diagnosis given the symptoms of vaginal pain, white discharge, and erythema to the vulva with tenderness to palpation. The presence of white spots tightly adhered to the rugae is highly suggestive of candidal infections, which are common in women of reproductive age.

Bacterial Vaginosis (BV): Although BV typically presents with a fishy odor and a thin, homogeneous discharge, it's still a consideration given the vaginal discharge and discomfort.
Trichomoniasis: This sexually transmitted infection can cause vaginal discharge, pain, and irritation, although it's less likely given the description of the discharge and the presence of white spots.
Vulvar Dermatitis: Irritation or allergic reactions could cause erythema and tenderness, but the presence of white spots adhered to the vaginal rugae makes this less likely.

Pelvic Inflammatory Disease (PID): Although PID typically presents with more severe symptoms such as fever, abdominal pain, and cervical motion tenderness, it's crucial not to miss this diagnosis due to its potential for serious complications like infertility and chronic pelvic pain.
Sexually Transmitted Infections (STIs) like Gonorrhea or Chlamydia: These infections can present with vaginal discharge and pain, and it's essential to consider them in the differential diagnosis, especially in sexually active women.

Lichen Planus or Lichen Sclerosus: These are rare dermatological conditions that can affect the vulva, causing pain, itching, and white patches, but they are less common and would be considered after ruling out more likely causes.
Vulvar Cancer: Although extremely rare in a 30-year-old woman, any persistent or unusual vulvar lesions should prompt consideration of this diagnosis to ensure early detection and treatment.