I don't mean to rain on anyones parade, but I tried vinegar on a sunburn once and it hurt REALLY bad and didn't do a thing for me. I asked around and at least according to those I talked to (two doctors in my family amongst a few others) it is just an old wives tale. I wouldn't try it as it is really painful.
Aloe works good, but as far as healing it more quickly and soothing the pain at the same time, the absolute best thing I have found is to make a salve out of comfrey leaves. Cool it in the fridge and then place on the burn. It will sooth and heal it very fast. You can find the directions on how to make the salve on the internet. It is easy, but if you aren't up to that sort of thing then you can buy a salve at most health food stores (although it won't be the exact same thing it will still help). During the summer we make a batch of it and keep it in an airtight container in the fridge for sunburns and emergencies (like if I burn myself cooking).
Good luck with your little sweetheart.