To be honest its not that easy if they are an established 2 - and you will need to commit to yourself and her that if it doesn't work you will still keep her. However it can be done and I have done it - but I have also failed in another case.
Some people may post to say that by taking on one you will merely encourage PAH to carry on buying in and selling - and that is true - however it is not that buns fault that she is there and my personal belief is that its unfair to let her suffer 'on principle'. I adopted two from PAH who were very miserable and had been adopted and returned 3 times in the past - and I have never ever regretted it even though in that case the proposed 'happy threesome' did not work out and I had to split them into pairs.. If I had left them there I would still think of them and feel awful.
If you have seen her (sorry not sure was it a him or a her??) and that certain bond has already happened between you and her then I think personally that you will always regret if you do not get her.