uh oh, now what?

Alright, so I brought the new cat home today. Before I left to get her I set up a room just for her so she didn't have to face our older cat or dog right off, I put in a litter box, a place to hide (under the bed), food, and water. All seemed well. I then went and got the cat, brought her home, put her in "her" room and sat down to read in case she needed anything. All of a sudden I hear hissing under the bed.

Yeah....our older cat decided to hide under the bed while I was gone...After about 10 mins I finally get the older cat out of the room. Not a happy cat. Afterward the new cat (bogurt) was very scared, which I can understand. After about an hour she came out to let me brush her for five moments then ran back under the bed. After awhle she came up on top of the bed and laid down against me, rubbing her head against my hand. I peted her and she loved it for a couple of moments, then suddenly she hisses at me and attacks my hand. I got alittle hurt but nothing major. The weird part? she didn't move, just kept growling from where she was. I was afraid to move to be honest. After about ten moments she went back under the bed.

So my questions are: Is there any way to fix the damage done between the two cats? And what is going on with her? I've never had a cat who reacted to me like that...I'm sure she's stressed, she hasn't had any water or food yet...Is there anything I can do?

She probably smelled the other cat on you and since their first meeting wasnt that great, well....

I would just keep them completely separated while she adjusts to the new smells and do the swap scents with each other, where you keep swapping towels between them. Let them get use to each others smell.

Intros do not have to be a quick thing.
You can take as long as you like. I know someone who takes up to a month and by the time the intros happen she just opens the door and all is well.

Both resident kitty & new kitty need more time to adjust. I give newcomer (adults) at least 1 week before I even think about starting introductions.

I was hoping to give them one to two weeks, but since our older cat kind of beat me to it, should I still wait, will it still do good or is the cat out of the bag, so to speak?

No they need to be apart. If their first meeting was good then it would be ok, but they didnt have a good meeting and definitely need to start over so they dont have a lasting bad relationship. I wouldnt even think about them seeing each other for another week. And then I would put some vanilla extract on their chins so they smell more like cookies than cats.

I agree with Pam - just pretend like the little encounter never happened & start from the beginning.