No it is not fair. I don't agree in the way her mother treated Barbara, but I do understand it.
The whole family business was dependent on Barbara, she was the only one integrated in the English society. Barbara did the administration including the accounting, negotiated with the suppliers and communicated with the staff. Barbara worked hard in the business so that they only needed one extra staff in the weekends (which saves a lot of money).
Beside this, Barbara was a very pretty and intelligent girl. Her mother must have hoped that Barbara would be an ideal candidate for a rich Chinese guy who knew what the Chinese traditions expected from him and therefore give Barbara and her family a much more comfortable life.
Barbara falling in love with me must have been her mother's worst scenario. She must have thought that Barbara would be taken away from her, leaving her alone in England. With no one to run the family business. And she might have heard about the reputations of the foreigners taking advantage of Chinese girls and then dumping them.
Also Barbara's mother had a very difficult life and had an unfair share of unhappiness. She must have lived under tremendous tension living in a strange country trying to survive as a single parent family with a daughter fighting for freedom, doing all kinds of things against her beliefs as a Chinese .
People should not blame her or accuse her. What happened to her is the worst what can happen to a parent and that is losing a child.
And finally, it wasn't because of her mother's actions that Barbara and I separated. Barbara's mother made our life difficult but not impossible.
(thanks to Natalie for the translation)