Booyhoo, you're right, marriage and children would have helped her, they would have had a stabilising influence. I am glad to read that they have been your saviour and you have escaped from your old life. Perhaps Joyce feared not being a good mother, of not having the discipline involved to do it, many friends had said that she was very messy, was her mind too haphazard to order her thoughts and she feared what would happen if she was not there for them?
I wonder if, in her mind, however she would have seen that as a sort of prison sentence, towing the line, an end to the dreams she held. She had acquired a sort of notoriety of being the different, exotic one who was always stylishly dressed and admired by men (a sort of high in itself) and that would end, to some extent without enough money to fund a lifestyle where she would have enough time for herself and her ideal of pursuing her dreams. Men would no longer circle her if she was attached and with children, her currency/demand would decline and she would feel stuck.
It might have also been that she felt financial pressure to never be dependent on a man and yet also wanted to a SAHM if she were to have children and never the twain would meet? If she had seen her father playing away from home and a stressed/depressed mother, she may have had an acute fear of being in a situation where they were strapped for money but with the feeling of having been destined for better things. Friends had said that she had had a good upbringing and it was felt that her mother's family had been of high standing in her country of origin. Had her sisters married very well and she felt shame that her life wasn't the same?