First off, I'd like to recommend the
Rabbits and Cats thread in the
Lagomorph Library that focuses on this subject. I think it may even contain my first post in '06 about it.
I first brought home my two kitties in 2004, as young babies. We didn't get our first bun, Maisie, until Feb of 2006, so our kitties had plenty of time to get used to their environment before the introduction of the buns (at that time, just Maisie).
My recommendation: Before introducing the kitty to Benny, make sure she's familiar with her environment, and feels comfortable around you. Since you mention that you're trying to find her another home, you may want to skip introducing her to Benny at all. It takes time, and a lot of supervision, and if you're able to just keep them separate, that would be best, if you're rehoming the kitty.
If you decide to keep her, however, you'll want to start out making sure your kitty is comfortable with you and her new home first. This might take months, but it's essential. Also, you'll want to make sure that Kitty responds to you saying "no" and such things, so you can handle any problems that may arise.
Another thing, you'll want to trim Kitty's claws, as she might bat at Benny in curiosity and mistaking various bunny actions as an invitation to a game. Benny will go right up to her, and she'll mistake that for an invitation, or get offended...and will result in a bat to the head. She probably won't use her claws to do it, but you don't want to take the chance.
Here is an excellent article on how to trim a kitty's claws.
So, once you've got those two things handled, you'll want to create an environment that both Kitty and Benny feel safe in. You'll want to create some sort of run/fenced-in play area for Benny while he's out, and have somewhere for him to run back into if he gets batted. Don't scold Kitty for batting...she's just curious and not sure what to make of Benny...it's totally natural. She won't understand getting in trouble for something like that. We've had buns around our kitties for the past three years, and they still bat when one of the buns hops right up to them. It's really offensive to the Kitty Code of Conduct (that says that you avoid newcomers at first, and introduce yourself gradually, and the first one living there gets first dibs on sniffing, etc.).
At first, you'll want to just set up the run, let Benny hang out in it, with toys and whatever else he enjoys having out with him. Let Kitty come to Benny in her own time. Don't put her in the play area with Benny...let her do that on her own. Might take hours, but it might just take minutes. Eventually, curiosity will overwhelm, and when Benny's got his back to her, she'll take a tentative sniff through the play area's bars.
Just let it take as long as it needs to...introductions will be in both animal's own time. Our kitties have never really adjusted to having the buns. The kitties basically just avoid the area while the buns are out, and (most importantly) I never leave the buns and kitties unsupervised.
Hope all that helps!