There are two issues being raised:
- How to plan character growth?
There is nothing to plan. Growth happens under any circumstances (except perhaps coma, hibernation and the likes)!
Your MC is above all a human being. She has the capacity to understand, analyze, think and plan. She can choose her most reasonable reaction to every environmental cue, be it to temporarily adapt to a demeaning situation, or to fight, full on, from the very first moment. She will grow from experience, and she will choose the path that is most suitable in her understanding of the situation.
From your description of the character, an introvert may first adapt and study the situation. She may identify breakpoints in those that wish to abuse her, and she may build trust with others around her who are being abused. She may slowly build the path to weaken the foundations of her cage, put her jailers in agony, and break free. How she does this, that is your plot, and for you to design. I sometimes work these situations backward: for instance, I plan that she will be free after she get her husband's mother to an asylum, which happens after she inherits her husbands fortune, which happens after her son dies, which happens after the husbands' creditor challenges him for a duel, which happens as soon as they hear that the husband ran away with the money, which happens after the husband receives a letter that the MC has forged telling him that he is going to be bankrupt, which is sealed with the stamp, stolen from the lawyer by that maid, with whom the MC has been very kind in times of distress, etc...
- the MC itself
Sorry for saying this, but the MC has the colors of a Natalie Sue in disguise. Being at the same time introvert, non-conformist, and righteous, and being a free spirit one day, and a caged prisoner the next, would be a truckload of flags if I were to review this writeup. I'd suggest to flesh out this character a bit better, make it more human, add a third-dimension to an otherwise flat collection of stereotypes.