She has agreed to let us take her daughter permanantly. She does not have the means to support a child as one needs to be. I already have 3 young children of my own but I am willing to do this. How do I go about getting it legal so that 3 years from now she can't just take her away. We already keep her more than she does but the thought of getting so attatched and her being taken away scares me.

Thanks in advance for the advice..

You'll have to file a motion for custody and/or adoption. A lawyer can and should help you with this.