It is always hard to walk in another's shoes. If it was easier there would be a lot less heartache.
You have been forced into a new reality, a reality your mom has been dealing with alone for many years. She is in reunion but is also for the first time allowed to openly show all the love she has always had for her child, but was never allowed to show in any way. She is different now, probably the most traumatic experience of her life is no longer a secret and she is free - her life sentence has been commuted.
Your new reality is the next phase in your life. You probably will not find anyone outside of the adoption triad who can empathize with you. Families were not meant to be separated, it is not natural. Could you also be going through a grieving period because you missed out growing up with your sister? I grieve for the lost time I could have had with my siblings.
I hope you find some way move forward, nothing in life is ever static, life happens and we have to find some way to get through it. Give your sister a chance, try to see if you can connect, you have nothing to lose and everything to gain.
Please try to know your sister...chances are she has waited her whole life just to have that chance.
Kind regards,
Dickons
P.S. Please read "The Girls Who Went Away" by Anne Fessler. It may help you understand what your mom went through. It helped me.
I saw behind me those who had gone, and before me those who are to come. I looked back and saw my father and his father and all our fathers, and in front to see my son and his son, and the sons upon sons beyond. And their eyes were my eyes. As I felt so they had felt, and were to feel, as then, so now, as tomorrow and forever. Then I was not afraid for I was in a long line that had no beginning and no end.
And the hand of his father grasped my father's hand and his hand was in mine, and my unborn son took my right hand and all, up and down the line thatstretched from Time That Was to Time That is Not Yet, raised their hands to show the link. And we found that we were one...
~ Richard Llewellyn