There are some very strange responses to this sad and difficult problem, and I wonder why.
I might be wrong, and hold my hands up if I am, but a woman who has previously had a close relationship with her mother (and presumably other family members) doesn't suddenly CHOOSE to abandon it. The coincidence of a marriage (and everything was presumably fine before it) with the withdrawal of contact points almost 100% to emotional abuse by the husband. That realisation must be terrible for a mother and grandmother to bear, but it happens more often than we know.
To the poster who said the daughter had colluded in the decision, I am sorry, but abused and bullied women don't get a choice to collude or not, they simply daren't or can't go against their husband's wishes.
But what can be done? Bodhi, do you have any contact with other people where your DD lives? Would it be worth a phone call to someone you feel comfortable talking to about this? I know it's five hours away, but could you envisage making a surprise visit on a day when you know your DD will be home alone and see if you can talk to her. Don't ring her, cos the phone will likely record the fact,and that could cause issues.
Now, all is not lost, necessarily. Your daughter needs to realise for herself that this situation is not "normal", and therefore needs to seek help for herself. The best people to contact are Womens Aid, so arm yourself with their phone number before you visit. They will give her advice on what to do if she eventually realises that this relationship is toxic. But as I said, all is not lost. If her husband is basically a decent man, he might not realise that his behaviour is controlling or abusive. He might be not a very strong person himself and not coping with normal behaviour. He TOO can be helped to realise how his behaviour is unhealthy and unkind for everyone. It will take time, I know, a close friend of mine is 5 years along the route of sorting out her marriage, but her husband is a changed man, and although they have been separated for most of those 5 years, the hope for the marriage survival is great. He had cut her off from her family, her friends, due to his own insecurity. He has learnt a lot through counselling and advice and fingers crossed that this year will be the year he moves back in with her and their children.
But first, the wife had to recognise that controlling behaviour is not "loving" at all, and she needs to be strong enough to say so, whilst still affirming that she loves her man, as my friend did.
I hope it all works out for you. Such horrible things usually do given time. But I know you don't want to miss out on a grandparent's or parent's pleasure, and I hope you don't for long.
Much love and sympathy, but stay strong and calm, offer what advice you can, and then step back.
If the DO seek help you will be much needed as a shoulder to cry on or a person to scream at during the times when it all gets very hard for everyone, and you will have to be a rock for your DD. Never take sides, this man must have good points for your daughter to have chosen him, but sadly they aren't surfacing right now.
And no, you are not an unsuitable grandparent whatever than implies.
Good luck.