Thanks. we are going to take her to the vets tomorrow, as they were closed by the time we retrieved her on saturday. The yowling has mostly stopped now, just occasional and I think now it is related to attention (she stops when we fuss her!)
I think it is going to take a long time for her sister to accept her again. Our older cat seems to have accepted her again, well she tolerates her which is really what she always did! However her and her sister were always cuddled up together and playing together, but now her sister hisses and growls at her. We are doing scent transfer and hopefully she will accept her soon.