Which version of Supergirl are you thinking about, and which version of She-Hulk?
You seem to be a relatively new or infrequent poster; if you're thinking about RED She-Hulk and some of her high end appearances, or DCnU (2011 to present) Supergirl versus, say, Jen Walters She Hulk from her Jupiter Suit era, there's a GREAT case to be made for She-Hulk. Ordinary Jen Walters She-Hulk? Not quite so much, though she stands a better chance than most respondents here are suggesting, if only due to Kara's natural restraint, fight inexperience, and tendency to brawl.
Most incarnations of Kara from the past 10 years ARE physically superior to Jen, though, making this Supergirl's fight to lose. (At least as you CURRENTLY have this written ...)
if you are not joking then this is the sole reason why no one would take you seriously. Even most Marvel bias fans at least know when to vote for a DC character when it gives them added credibility.
This is a purposely spite thread. You the only one don't know it, unless you are joking.