Hello Rose, and a warm welcome to you.
It's such a shame that your daughter doesn't contact you and to be in a cult if that's what it means, then her loyalty is with the leader and to stay away from her blood family.
Whether or not this marriage has been arranged is something you don't know and probably won't be able to find out.
The reasons why all of this happened could be for a number of reasons so I wonder whether she was suffering from depression and this group suddenly appeared and offered to help her by joining because she may have been pleased by the way she was treated.
It could have been she needed something more out of life or a friend introduced her so all of these are plausible but also questionable.
I know how sad it must be for you to know she is getting married and you're not involved, that's upsetting, but please if you could get back to us and give us a little more information.
It is hard when any child grows up and leaves home, which they tend to do, for employment, travel, to form a partnership, a host of reasons. As a single mum your daughter would have been such a large part of your life (and you hers) and now it seems over.
A loving child will try to keep in contact and try to consider the parent's feelings if they can. It does not look like it is happening here. Being brought into a cult does tend to separate the person from their previous life and that is sad, frustrating and worrying.
Unfortunately I can't see any actions you might take provided no violence or obvious coercion was involved.
One thing. You daughter knows you as her loving mother, and you have not changed. I guess if she is ever in need, or the attraction of this church wears off then she will remember.
For now I'd suggest you try to look after yourself. You mentioned depression so I'd suggest seeing your doctor and having your condition monitored.
Do you have friends or family you can be with? Not being alone does make a big difference.
Are there any ventures you had been putting off or thinking about? Around now may be the time
I'm really sorry to learn that you are having such a tough time. I can't even imagine how hurt and angry you must feel. I'm sure you are also terribly worried about your daughter and the changes in her behaviour.
The others have already provided good advice. What I want to add is that if this was happening to my daughter I would want to know everything I could about that church and what goes on there.
What do you think would happen if you asked to go to church with her? It won't stop your pain or the wedding but at least you'd gain a better understanding of what you're dealing with, as I suspect there might be a long road ahead for you two.
Kind thoughts to you