I am 32 live in Virginia. My dad died when I was 10. My mom and him were separated and in that time he got a women preganat. I am not sure of the pin pointing details but what I was told is that somehow she got taken away from her mother and put up for adoption. Her name was Grace. After my dad died my mom said she got in contact with I think the agency( which she says she no longer remembers) to maybe adopt her but the little girl was already in a nice home and had been since being taken away from her mother and they wanted to adopt her. So my mom did not want to disrupt her life since that family was all she knew.
So I guess my question is with so little info how would I even start to find her?

Your only options, really, are to hire a licensed private detective (expensive!) or to post on reunion websites.

I believe that ISRR allows for a search for people that is not necessarily the parent/child relationship.

Please remember that she may not know she is adopted, and that searching for her could disrupt her life. If she DOES remember her birthmother, the fact that she was taken away from her usually means that there was something bad going on that endangered the child. If you do find her, make sure to have your initial contact through a neutral third party (a pastor/priest is generally a good choice) before barging into her life.

Please also remember that you may be related by blood, but NOT by law, and you have absolutely no "rights" to find her.