Very nice match-up...
If it were a ring-referee-rules kind of match, I'd see Graf just edging out Sabatini, as (to me) she seems to have more technique, brute strength and toughness...
... BUT, if it's to be and all-out, anything goes catfight, the Gabi takes it, since she's only just a small notch behind (or just about equal) to the german in the aspects I've just listed above, but would be ahead of Graf in two other matters.
Despite being pretty much a "good girl", I would see Gabi being the one who'd be more willing to fight dirty and, god forbid (for Graf !) that any "naughtiness" would make it's way into the fight, as Sabatini has the definite advantage there !
http://celebrityimg.com/photos/GabrielaSabatini34099.jpg