To me the character seems developped enough and your problem lies elsewhere
It seems to me that your player, no matter the number of words in his background, has a very precise idea of where his character comes from and how it influenced her development.
The problem seems to be that the resulting character results in a very "edgy" character that does not mesh well (or at all) with the rest of the group, the NPCs of Barovia, etc.
It's that kind of character, that I personally saw too often, which kind of makes no sense in the world. How would have such a character survived, after basically being (and pardon the language) an asshole all of her life, to everyone around her ?
The fact she had a hard life does not excuse her behaviour, especially considering how those she abuse might have just as hard a life ... sometimes probably even a lot harder, it being Barovia. How come they don't just organize a mob to hang the abusing thief ??? That is what I would expect to happen, both IRL and as the DM in this instance.
In fact, when my players do such careless stuff that ends up 'hurting' a lot of NPCs I will always have at least a couple of those NPC victims become vindictive towards the PC and/or the whole group. When organized well and in a way that makes the reasons clear to the PCs, this often leads to epiphanies/change in behaviours from the PCs.
But that's not even the real problem. We can and do often suspend disbelief on such characters to allow a player to have his/her fun.
No, to me the real problem is that the way this character is played is not engaging to the rest of the group. In fact, quite the contrary, since it does seem the rest of the group is put off by those actions.
I wouldn't ask this player to refine the character's background, since my experience with this solution is to find that my player has in fact 'doubled down' on the character's edginess. More often than not, asking the player of a 'difficult character' to refine its background in the hopes that it will solve such problem only gives the player more arguments to respond to any of their fellow players' concern with 'that is what my character would do', aka the 'my character syndrome'.
Instead, what you need to have your problem player realize is that D&D is a collaborative story telling experience ... and that his character's behaviour is problematic simply because it repels the other players. Plus, it probably wastes a lot of everyone's time for events that lead to (in my own opinion) bad story telling.
As a player, spectating while a comrade is being abusive to widows or stealing ale makes for a very boring chapter in our common story.
As the DM, you are the referee in such matters. I would do as I so often did, aka start by letting the player know I feel the need to talk to them in my capacity as referee. I'd try to be as diplomatic as can be, but there's no dancing around the fact that these events are boring for everyone except maybe the 'culprit'.
I don't shy away from speaking on behalf of my other (majority of) players ... even if/when they don't complain to me directly. I know that I easily can make the difference when the whole group is having fun VS when most of the group just silently goes through the motions, cultivating their patience.
No, I would be polite but firm, I would go straight to the crux of the point: this behaviour doesn't make for a fun or engaging story, is also not something the rest of the group can or wants to engage in. And also, from an in-game point of view, this could lead to danger for the character in question, once NPCs get fed up with being abused and decide to grow a spine (or a mob).
If the player does not get it or does not want to change his behaviour ... well, to me this is a proof that this player does not want to engage in any kind of cooperative storytelling with his fellow players or even me. Faced with such players, I politely suggest that they might enjoy playing single player video games and/or politely kick them out of my game.
All because I know from experience that it is only a matter of time before the group dissolves when 75-80% of the group is not having fun for long whiles every session.