Amethyst, the “adopted” (not legally and she has adopted when she was already 19 years old) daughter of Derpy/Dizty Hooves, Doctor Hooves and Screwball. and the adoptive big sister og Dinky Doo and Emily (Will explain who that is in the next deviation)
Warning for child abuse below (Not 100% if it counts as child abuse? but still putting the warning)

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Amethyst was born too ponies, her first few years of her live were rather okay, though when she turned five her father just upped and left, with no explanation. She and her mother haven’t seen him since, soon after Her mother starting falling apart emotionally) and went to food as a comfort which lead to her mother getting various inflections and illnesses and treated Amethyst more like a servant than her child, which prevented her from looking after Amethyst probably, which lead to Amethyst being heavily neglected, Amethyst grew into a teenager and often would see teachers as parental figures because she didn’t really have any, though none of them really were like parent figures to her and because of the fact she was technically not a orphan (though she was felt like she was emotionally) no one adopted her emotionally or legally. Amethyst started to eat less and less because she started to gain a fear of gaining weight (anorexia nervosa) because of the fact her mother was gaining more and more weight, that at this point she barely wanted to even walk. Though in Amethyst’s mid teens, Her mother meet another stallion and formed a relationship with him (and got married and had a foal with him), at first (first few years of this newer marry) his stallion seemed decent enough always treated Amatha (Not sure if I should give her a design or not) (Amethyst’s half sister and his biological kid) alot better than Amethyst and always played favourites with them, near Amethyst’s 18 birthday her mother died (she basically ate herself to death) and although Amethyst had moved out already and was trying to study a degree (it took alot out of her to get good enough marks for her to study a degree, because her lack of attention when was younger affected her development alot), the stallion (The one her mother married when Amethyst was in her mid teens) started to dump the responsibly of raising her half sister on her, which caused her to not be able to study for a year and whenever he would look after her half sister she used her as a meal ticket (her half sister).The nest year though her mothers sisters/relatives finally stepped in (they didn’t try to help before even though they could). Amethyst went back to studying though at that point (according to her) had no family and was still anorexic (which was true). One day, she bumped into a little filly, named Dinky Doo that was asking random adults to act as her sister so she could participate in the sister hooves day (the episode where Rarity pretended to be Applejack for Sweetie Belle in the Sister Hooves Race, I think? not 100% sure though), she thought this was a weird request, though decided to pose as Dinky’s sister as she often would try to cheer up/make children happy because she was rarely happy as a child. She did the race with Dinky , and even though they didn’t win Dinky as happy she had a sister for a day. Amethyst thought that after the race Dinky would just go on and forget about the random mare that pretended to be her sister (Amethyst) (She wasn’t to happy about it), though that night Derpy, Doctor Hooves and Screwball (Dinky’s parents) invited her to dinner because they wanted to thank her for pretending to be Dinky’s sister, because as Amethyst found out, many fillies made fun of Dinky because she had no one to race which with and that she didn’t have too many friends because of Derpy’s and Screwball’s “oldness”. Amethyst soon later moved closer to them and started to hang out with Dinky alot, helping her with homework, doing projects with her and basically becoming a big sister to Dinky (emotionally), Amethyst also started to see Derpy, Doctor Whooves and Screwball as parents and they did act as parents to her and they “adopted” her (again emotionally because I don’t think you can adopt a adult in the means of law).
Amethyst cut all (almost except with her half sister) ties with her biological family, she finished a degree and set up a event planning business, she was finally content and she started to gain weight (started to fight her anorexia), she finally had a supportive and caring family, she now had proper parents, a new adopted sister and adoptive sister (Emily and Dinky, as I say above will explain who Emily is later)

First picture is her at 19 - 21
Second is after that
Third is now her hair is currently in the Cookiestarverse.