This is on behalf of a friend....
her husband slept with someone else and the result is a child who is less than a year younger (or older, I forget) than her own second child. Her husband told the OW that he was married in the hospital after she had given birth, he did this so that she would not choose to have a termination 
He told my friend about his infidelity and the child some years later when she was pregnant with their 3rd baby. he told her because the OW had contacted him and said that he was allowed contact with their daughter. She had previously not allowed contact.
My friend chose to stay with him. He went to visit his child weekly for a few hours with the OW, as she wouldnt allow unsupervised contact. She has over the last 4-5 years intermittently stopped and started contact.
My riend and her husband now have 5 children. 'D'H has told their children about their half sister and they have started to go with him to visit; not to the house, but as I understand the OW now allows unsupervised contact. However, she will not allow her dd to meet or have any contact with my friend, she is not allowed to their house.
This means that every week for a couple of hours on a Sunday, my friend's DH and their children go off without her, pick up the half-sister and go for a day out/trip/whatever. She is upset that she is being excluded from her own family in this way. I think it is completely out of order. Isnt it?
Surely the child has much to gain from being welcomed into her fathers home and his family?? And I dont think it would be unreasonable of her to insist that she be included/child visit their home? She says that OW will not allow it and it may jepodise her husbands access....
we were discussing it last night; she is upset, it is driving a wedge between them. I advised that she contact the OW and maybe then she will feel more comfortable about her dd meeting her. So far OW has refused to meet her. I said she should post a note through her door and then knock the door when she has had time to digest...
Any experiences/advise/insight greatly appreciated 