Britain is not and was not a dictatorship. Margaret was a big girl. She could have married him if she had wanted to, but it would have meant giving up her royal title and perks probably. I guess she loved that life more than she did Townsend. She made her choice, and I think that choice made her miserable for every day of the rest of her life.
Here's hoping she's with him now.
True, but she also would have lost her family by marrying Townsend, as they undoubtedly would have disowned her.