Initiating Contact - After Fostercare

We finalized the adoption of our children last month. Mom was incarcerated the entire time the kids were in custody. We never met her, had very limited contact with her on conference calls during permanency meetings, and sent her letter updates. She never wrote us - only the kids. I sent a final letter to the SW asking some questions, stating that I would like to keep sending letters/pictures, and giving an email address. It has been over a month, and I haven't heard anything. I was finally able to get the SW to give me her address now that she is out of prison. However, I do not know if she sent the birth parents the letter. How long should I wait before sending another? I was thinking of waiting at least another month, (get past mother's day) to giver her some time, and also to give us time to get a PO Box. I would also appreciate any suggestions for groundrules for our relationship going forward - I'm not sure about contact with the kids for a long time due to their history, but I want to be able to answer questions the kids have too. We do have an ongoing relationship with their younger half-brother and his paternal grandparents (who think of my two as their grandchildren).