Birthmother terminally ill & wants to see me

I wonder if any of you can help. I met my birthmother a few times about 12 years ago, the relationship didn't work out for various different reasons. I was her second child and adopted, her older child was fostered and he kept in semi contact with her. When I met my birthmother I also made contact with my brother and we have always stayed in touch. We get on really well & won't be without each other. He hears from our birthmother once in a blue moon. We have just discovered that she is terminally ill & wants to see us both. I said I would go to support my brother but as the day is coming nearer I really can't face opening up old wounds. Part of me feels so sorry she hasn't got long and it's a dying womans wishes to see me the other side of me can't face it at all. I'm hardly sleeping & feel quite sick about the whole matter of the visit. I don't really know the woman, I feel disloyal to my adopted mother the emotions just go on. I don't know if I will regret it if I don't see her as she has only been given to the New Year but I know I don't want to start communications again if it is longer (which sounds awful). If anyone can offer any advice it would be much appreciated.