Aggressive new pig

Question
We lost a guinea pig about 2 months ago, and recently decided to again add in a 3rd pig to our herd.  Our girls are about 1 year old.  All our guinea pig's over the years have been raised from babies.  Our new pig is not a baby, and to best estimate is about a year old.  She was selected as a rescue pig, and was being kept alone in a small cage.
When she is with people she is sweet, chatty, and inquisitive. We have had her in quarantine, and she has 5-6 hours each day in a large play pen with lots of hidey spots and tunnels. We started the integration with our other pigs by putting 2 playpens beside each other so the pigs could see/hear each other but not have direct access.  The new pig teeth chattered/puffed up/squealed but that seemed to decrease over time. When we tried a brief integration, our sweet new pig, repeatedly and continually attacked the other pigs drawing blood. One pig is a total submissive, and the other will challenge the new pig occasionally.  We gave everyone a break then started the whole process again more slowly.  The new pig teeth chatters non stop, will stalk the other pigs, and continually attack drawing blood. She becomes so agitated she will attack one of us if we try to remove her, and last time had to be picked up in a towel.
The pigs could not be left alone for a second or the new pig will rip them to shreds. The new pig seems lonely at times, and will spend long periods of time in her cuddle cup or pigaloo.  She seems happy to go into her playpen from her smaller cage each day, but at this point I can't see her with the other girls.  She is sweet, and has never bitten one of us or runs, the aggression is only toward the other pigs.  She has been eating/pooping with no concern, and does not appear to have any illnesses.
Suggestions please?  We have never tried to integrate an adult into duo, and I'm not sure if the personality of this pig will allow things to develop.  We would like to keep her in our home.

Answer
wow a nasty one

well there are a few things, usually the process you have done already would be enough, there would be some fighting but adfter a short period of time a boss would be decided and peace would follow. sometimes however you just dont get that.

you were right to start the familiarizing, though i would take this a step further, if possible devide the hutch/cage where the duo live, one half is the newbie's the other the duos, idealls you want it to be wire mesh so they can see and smell each other. everyday sway them over, this way it mixes up the scents and forces them to learn to accept each others smell.

now for a really aggressive pig like that you have to get her to appreciate the other pigs, and the best way to do that is through fear, a shared box on a noisey, bumpy car ride works well, a wire pen surrounded by barking playful dogs and no hidey holes, a noisey bath tub complete with water. you can get as creative as you want with this but basiclly the trick is to make her aware of how much safer she feels with the others.

other things such as cleaning out the cages and washing the hutch, toys and houses with mild disinfectant are also important when introducing them so that their home is neutral to both parties and lessens territorial tensions.

finally there is a small, very small chance that your pig might just not get along with others, it happens to one in a hundred but there is always that chance. but keep at it and remember fear is the key

best of luck

ps. sorry about the terrible spelling, i couldn't see the screen very well as i had misplaced my glasses and the keyboard keeps throwing in letters