Debbie,
Have you gone thru the Social Security Office??? If you know the names that your mother was using, including her maiden name, birthdate,etc....You write a letter to her, I dont remember if the envelope was to be sealed or not--then you place that into another envelope and take it to the local social security office, and they will take the letter and forward it to your mother.
My father was looking for his sister, one that he had not seen in 30 years or so, and his siblings claimed that no one knew where she was, he found her that way. The ss office called my dad the next day to say that they had found her and if she wanted to contact him then it would be her choice.
And an old man that I knew was looking for his daughter that he had not seen in 25 years, found her thru the ss office, and she and I have had a friendship now for about 6 years. She also was found the very next day.
Good luck in your search.
Cindy.