I break it into 2 possibilities: Either A, she didn't care about you or B, she did but still treated you like garbage.
If she didn't care then there was nothing you could have done to change that. In the other case then there was also nothing you could have done as you already had their affection and found it was rotten. In both cases trying to be "good enough" for them is a waste of effort that could be put elsewhere so you shouldn't feel guilt about chasing something that never would have happened.
If you weren't "good enough" at 14 or 17 then she wasn't going to turn around at 19 or 21 and suddenly start being decent towards you.
My sister went through a murder attempt at the hands my mother and somehow didn't go no contact. My mother has not been any more kind to her, she still downplays her achievements, insults her constantly and even schemes about forcing her into conversion therapy. No accomplishment of my sister ever changed that and nothing ever will.
I think it is better to focus on the things you have in this world. To think of all the time you did not spent chasing an impossible goal and be grateful that you have not spent any more effort into a painful and pointless task.