I think for a story like this, good characters are the dealbreaker here. I’m not exactly sure what route you wish to take the story down in detail. But, I think the important thing here is to make believable characters, each one being unique in their own sense. Obviously, good characters is a must really for most, if not all, stories. With the story you’re talking about, I think you need to work hard on the characters.
Another thing I would do is try to make the main character’s past very mysterious, but slowly give hints or answers to the readers who are questioning their main character’s past. While my story isn’t whatnyours is that I’m currently writing, my character too has a very dark and secretive past. I’ve put a lot of time into thinking her through almost fully, which is something I intend to slowly reveal to the reader. Try to really flush out the past as much as you can. You might not need it to be this huge thing, but think it out enough that you pretty much have it all decided. It’ll help with dropping hints to readers later on.
The last thing I’d probably do in your case is make sure that you have enough elements are your main character’s surrounding to make a story. Sure, the main idea is one with a past that haunts her that she doesn’t want people to know and it’s going to be about building trust with others. But that’s not enough to keep the story afloat. You need to make sure you have enough plot points or elements in between to keep the story going. I’m currently in the process of getting some more short and long term stuff in this regard for my story I’m writing. I have the general overall plot line figured out. But that’s not enough. I have to have things in between to make the story continue and flow. In my opinion, this is the hardest, and most crucial part. When you have an outline, it seems great. But once you get to writing, you’re trying to figure out what to put in between the plot points, figure out pacing, smaller subplots, etc. It’s difficult, but it’s really important. If you don’t have enough interesting or compelling point in between the major plot points, some readers may get bored and decide to stop reading the story. So it’s so important to nail this part.
Other than that, make sure to have choices in it. They don’t all have to be huge choices, but something where the reader gets to decide certain things other than outfits. At least, I look for that in a story. Otherwise, I think that’s really all I have to say about that. Hopefully this didn’t sound too rough. That’s just the advice of give to someone. But I’m not a seasoned vet with stories on here: I’m writing my first one still. But that’s what I’m looking at with my story. Good characters, good plot, and a lot of stuff in between