karearea

If shes just had a shower and well and clean down there before you start then it could be her just getting really wet. My girl does the same thing occasionally when I'm going down on her or after a really good "workout". If it doesn't really have a strong foul taste, she isn't in any pain or discomfort and it's not there permanently, then in all likelyhood it's nothing serious and just natural secretions.
But if it's there all the time, ie when she's all showered and clean and you can still see it, feel it especially(like a lump or cyst) then follow the above advice. Get her in to see her doc. Esp if you're both worried it's something more...