"Sadly, women in ancient China had no sense of self-respect."
I'd like to disagree with this statement. When you say this, you are already thinking in modern terms.
My area is European Middle Ages and at that time a woman had no power over her body. She belonged to her father, then to her husband. Does that mean she had no self-respect? Where does the sense of one's worth sprung from?
I have read chronicles and even some 'biographies' (in the shape of a collection of documents that give insight into their lives and struggles) of women. True, these were mostly high-class women, but let's start there.
From what I could see in these documents, a woman's worth was tied to what she could do. There's the case of a young queen whose husband had quite a few well-know mistresses, but she took all the bastard children under her wing and raised them. At this point, instead of being a victim, she was in-charge and the mistresses effectively lost control over the lives of their own children. She was also capable of governing a large set of estates. Her worth and self-respect was not tied to submitting without a word to her husband's behavior.
There's another case of a woman who rose to be in charge of a small convent. She faced mutiny within the ranks, and pressures from outside, and yet she rallied and went so far as to go in person to see the Pope (or his representative). And yet, she still willingly submitted to and reinforced attitudes we today abhor.
To focus on your example: Perhaps bringing her husband a mistress is precisely a sign of how much self-respect she possesses. She does not wait for him to choose someone, but chooses someone herself. Someone whom she knows will please him - kuddoes for her because she knows her husband's taste and will only give him the best - and who will also please her, in the sense the mistress will recognise the wife as her 'superior' within the household and must strive to please not only the husband, but also the wife.
Or perhaps, as some lady in the 19th century once wrote, the more mistresses he has the less he'll come to bother. If there is no love within the marriage, making sure the husband is sexually satisfied means the wife can focus on having a respectful, or even friendly, relationship without the unwanted intimacies. Just imagine yourself forced to partner with someone whom you respect intellectual - perhas even enjoy spending time with - but for whom you have no sexual attraction whatsoever. Wouldn't a lover to handle the sexual angle be the perfect solution?
she submissively concludes that her only role for the rest of her life is childbearing.
Is that historically accurate? Is she forced to fit in the role, or does she feel fulfilled and ready to start a new stage that she expects will bring her equal fulfilment? It is not uncommon to hear of women who give up their jobs because they want to focus on being mothers, but men sometimes do it too. Have you ever heard of men who give up a job or just a time-consuming hobby because they are ready to become parents and that means moving on?
This change doesn't have to be free of ambivalence. Most new-parents miss the freedom of before their children were born, no matter how much they love their babies. Even if she willingly embraces this new phase, it's perfectly normal to miss and, at sometimes long for, the freedom of the past. That, however, does not have to erase the satisfaction of treading this new path.
Keep in mind that, in a world where women are supposed to go from being a father's possession to a husband's possession, anything that breaks the mold had the potential to be extremely fulfilling. She has satisfied her desire to do more, she has earned the respect of her peers (at least some). Perhaps she truly is satisfied and now wishes to do what else she wants to do - which is to be a mother. Even today there are women who are soldiers and risk their lives, and yet still long to be mothers. Why would she be different?
Finally, do not assume that the self-respect of a woman in the far past is dictated by the same as today. Nowadays, we cannot conceive of not having power over one's own body. In the past, you grew up with that idea as a given. As sure as the sky was blue! Your sense of respect was not tied to your body, but to your actions. Whatever you could do, that is where your sense of respect would come from. If your historical character got her hands tied and was forced into a role she did not want, even then that might not take away her sense of self-respect. She might have seen it instead as a tribulation to be faced with dignity, making sure she could control as much as possible within her limited reach. And, believe me, for some people who live in the greatest restrictions, the ability to take control over the smallest detail will bring forth a sense of self-respect. Because they can still act of their own accord.
In conclusion, do not show this culture as a piling of atrocities. Things are the way they are and the reader will easily see how wrong it is by today's standards. Instead, show how the oppressed women manage to find the strength to pull themselves up and be proud of who they are and of what they have accomplished.
PS: I'm not saying there weren't quite a lot of women suffering terribly and possesing very little self-respect, believing they were worth nothing. I'm not saying there weren't quite a lot of women who longed to live in a different society. But most would eventually learn to comply... and either bow their head, submitting and dragging themselves through a painful life, or lift their head as high as they could (or when they could) and fight to control what little they could control.