Who can help me find a way to have a relationship with my granddaughter?

My son had a daughter by a girl that he had a casual relationship with, we had a good relationship until she got married now she makes herself unavailable to us. We are not trying to bother her or her new husband or family we just want to be able to have a relationship with our granddaughter. We want her to know that we love and care for her what can we do or who can we talk to to keep a relationship going with our granddaughter?