spetznaz
Senior Fanboy Killer
Spiderman would win.
And here is why.
Cassandra is one of the best hand2hand (human) fighters in DC. Second only to Shiva. And based on BatGirl: Knight Alone she is so adept and fluid that she seems to move '4.2 times faster than baseline human' and have strength '2.6 times baseline.' This is according to the Feds who were viewing tape of her basically thrashing a whole room of armed Special Agents. They thought she was a metahuman due to her speed.
But she is not metahuman. It just that her training has reached perfected levels.
But this is Spiderman we are talking about.
He can lift 10 tons, has superspeed (not Flash level, not even QuickSilver, but still considerably faster than the average person).
Hence physically Spiderman is just too much for Batgirl.
Whcih brings up Batgirl's greatest weakness. She does not have Batman's mind. She may be better than he is in hand to hand combat, but she is not near the strategist he is. Hence she would have to rely on her (great) physical prowess against Spiderman. And that would not be enough.
It would be an interesting fight though. They both have super senses, can both detect and dodge projectiles and bullets, and all that stuff (Batgirl is basically like DareDevil-lite when it comes to senses).
And Batgirl does have the uncanny ability to 'predict' what a person will do. And that is a great advantage for her.
But Spiderman would need more than sheer physical strength to defeat. For example Batman and/or Slade could take down Spidey, but it wouldn;t be through hand to hand combat. It would be through strategy and prep time.
Batgirl would rely on her physical abilities, and even though they are amazing Spiderman is a 10 ton strength metahuman.
Batgirl would fight valiantly, but she would fall.
I love everything about Cass - her attitude, skills, costume. But Spidey is a meta, and unlike Batman (whose greatest weapon is his MIND) Cassandra's greatest weapon is her amazing combat skill. Tat would be more than enough to beat human opponents (even skilled adepts like Elektra), but Spiderman is a meta.
A perfect fight for Cass would be against DareDevil. They are quite similar, with the differences being that DareDevil's 'radar sense' is more honed than Batgirl's proximity senses, and Batgirl's fighting ability is better than DareDevil's. Would be a great fight.
Against Spiderman Cass would need Batman's mind more than Shiva's fighting ability.