is she wet enuff? if it is not it may be the cause.
if it is wet, but still feel the pain, it may be some sort of
infections.
woman's cheebunz is very frigile. If you are too rough, and try to
be too kinky (like finger-f8cking with more then 3 fingers) it may
hurt it. the hurting may not bleed, but it can cause
inection.
beside, has she always been having a lot of discharge? See lately
got more or less? If more and more strong smell, it may be
infected.
go see a doc early. if not can affect health.