The vulvar skin can thicken for a long list of reasons, and I don't think it's terribly uncommon for this to happen. Genital warts most often don't present that way, but some other types of HPV might. Again, though, no telling what could be the cause. Lots of non-HPV possibilities. Warts can show up weeks, or months, or years after someone contracts HPV, but most often within 7-8 months.
You know, it's hard to offer much guidance with your partner. You haven't been officially diagnosed with much of anything at this point, right? It's so frustrating when the diagnosis is this unclear.
Keep us posted if you don't mind, and let us know what you find out.