What I have found is that once we are able to establish a relationship with our child that is all our own, resolution does come. Send letters and pictures of yourself, give her the knowledge of you. The feelings of failure you have are not necissarily grief related. I think that they are more related to shame. Shame is an issue that is not really talked about in adoption, but for birthparents it is a more difficult issue to resolve than grief.
Shame is more than the normal guilt one feels with a loss.
It can effect the way you deal with your open adoption relationships and relationships in general. You may find yourself being judged unfairly by family and friends. You need to know and truly believe that you are a good person who did the best with what you had at the time. Here are a number of written resources avaliable to you to help you through. I have also written two issues of Open Adoption Birthparent on Grief in adoption.