Sounds like an allergy to something. Does your partner use any toiletries down there - creams, lubricants, cleansers, scented products? What does she wash in besides water? Consider also what she washes her underwear in. Maybe ask about face toiletries and cosmetics too because you probably kissed. What had each of you eaten? What toothpaste etc. do each of you use? Be careful to have antihistamines with you, just in case this flares up again unexpectedly. If the swelling starts and does not appear to be stopping or seems to be spreading to your throat, call an ambulance immediately
Hello, if it continues, I would see your GP to rule out anything serious.
This is almost certainly an allergic reaction. I'm not sure if you're asking if this is an STD, but no STD gives immediate symptoms like that. It's either an allergy or some sort of trauma to the lips. I hope it has resolved at this point.