My husband has a 3 year-old daughter. She lives with us for over a year that we've been married. In November 2010 he got sole custody of her. And basically her biological mother didn't see her ever since. In may 2011 she had another baby and the state of Maryland had the custody then it was given to her baby's father mom. She been on methadone program but was still taking drugs and was caught doing it. Right now she is on probation basically for stealing and she also might be in jail at this very moment (we not sure) for another case of stealing.
So I want to know what do we have to do to terminate her parental rights and how can I adopt her.

I don't see grounds - what State?

Have you asked the mother to sign to permit your husband and you to adopt her?

Maryland
And no we have not seen her for like a year.

You have the order reversed. You want to file for adoption. As part of the adoption process you ask that the mother's rights be terminated. You need an attorney to make sure the adoption is processed properly. The attorney will take care of getting the mother's permission or an involuntary termination of rights.

Agree, the first step is the attorney, get all the adoption paper work done, the attorney contacts her and tries to get her to sign over her rights.

If she won't sign, then it gets tough, and you have to take her to court to take rights away.

As long as she wants some contact the courts may not take it away, they may order supervised visits.
Now also with a history of drug abuse, no contact with child and perhaps prison, they may take her rights away also.