I first I thought it was Strikeforce's doctors, but after finding out it was her personal doctors, this cancellation reeks of BS.
Carano’s manager, Scott Karp, told MMAjunkie that HER OWN doctors advised against her competing and that was what caused he to withdraw from the scheduled bout with Sarah D’Alelio.
Blobbin out 
ulcerative vaginitis
Because her boyfriend didn't?
lets have her medical records published so we can get to the bottom of this.
Coker confirmed that Gina was "ill." Don't know what that means though.
MattBenwa - Because her boyfriend didn't?
LOL
I read it had to do with her contractual obligations to the movie she was in. I'm guessing they don't want her showing up at the premier with a black eye, also if she looses it could impact the interest level in the fight. In addition, Zuffa probably knows that she will be an even bigger draw once the movie is out.
My guess is a combo of contract obligations and zuffa being a lot better at promotion than strikeforce.