There are thousands of comments, thousands of questions that need to be asked. How to begin?
Andromeda's dilemna reminds me of Harry's when he was talking to Dumbledore in book 6 about the nature of prophecies. The prophecy says Harry was to defeat Voldemort or be defeated. What choice does Harry have in this. Is he forced to act out a role he does not want to do? Likewise Andromeda feels she must carry on the family tradition. What choice does she have? Dumbledore points out to Harry, that Harry would have chosen to pursue Voldemort even if he never heard of the prophecy, that Harry always has his free will. Andromeda in your story has discovered her free will and realizes she has to deviate from her families plan.
As to why your story reminds me of Harry I have no clue.
Your story makes a big production on the question why. I suppose it's because it is this thinking that makes Andromeda realize it is she who has changed not her family, but the first time I read it I thought the whys, did she expect an answer, is there an answer was tedious.
The better question was how? How did her family change? Or how did she change? Your answer that her home was now stifling her seems incomplete. What event triggered this if it wasn't Ted.
Reading about her parents' deams for her remind me of the book Close Relations by Susan Isaacs..The heroine, Marcia rebels against her aunt's desire that she marry a wealthy well bred gentleman by living with the opposite. She would feel as stifled as your Andromeda if she did what was expected of her. But then she happens to meet a well bred gentleman and she likes him in spite of the fact that her Aunt approves of him.
What I'm trying to say is that in your story, we aren't given the reason of why her parents are so awful. We 'know' they are irrational purebloods, but your story doesn't hint of this. The parents could be normal people who just want the best for their daughter.
I am not certain that even in the pureblood world of the Blacks that it is necessary for the witch to always engage in meaningless dialog and always defer to hubby. This is not how I see Bella. I do agree that there would be a certain amount of deference but it would be to an idea and that both husband and wife would be equally constrained.
If we didn't have the Harry Potter background, Andromeda's thinking might be that of any 17 year old that is afraid to commit to the responsibilities of adulthood. For some people responsibility means loss of freedom or a curtailment on ones own personal rights. Granted in your story, you are portraying adulthood as vapid, but having grown up in the 60's I can assure you that the young can misunderstand the older generation.
The ending of your story reminds me a little of Huckleberry Finn who was willing to damn his soul for all eternity to save Jim. Granted all she was saving was herself in your story, but at least she realized the magnitude of emotion that would follow.
Anyway this was a story that provoked a lot of thought.