Don't - not your fault. Piggies are much more complex creatures that you'd expect. Finding the right partner especially this year is very difficult. I have a whole cupboard full of failed bonding t-shirts. ~
All you can do is try and - if you can - rescue date with the option of returning the dated partner if the bond fails in the later stages of the bonding process. Otherwise it is down to plan B, C or even D... With my Beryn I am down to about plan H or I after the only companion she ever tolerated died from a sudden heart attack a year ago - and finding Betsan took 1 1/2 years.
Be upset but don't feel guilty. Mixed gender pairings stand and fall with being able to establish a mutually agreeable hierarchy. This has clearly not happened in your case. But you will never know before you try. Every bonding is down to riding the tiger. Unfortunately you seem to have ended up with a girl with some major fear-aggression/socialisation issues by the looks of it, caused by her own background.
It is unfortunately a myth that all mixed gender pairs work out - they largely do, but only once the initial all important hurdle has been taken, and yours have unfortunately fallen at it.
Moody guinea pigs: Depression, Bullying, Aggression, Stress, Fear and Antisocial Behaviour
A Closer Look At Pairs (Boars - Sows - Mixed)
For the time, just put in a divider between them and then - once you are over your upset and are no longer knee jerk reacting -, think through your possible options.