This would take place before the first Equestria Girl's special and Sunset is still a bully and Sunset could be a bit naive of certain things still which makes her misunderstand some things at times. This would be one of those times as Sunset is picking on Fluttershy and actually looks at a flier inviting people of all ages to come down to the animal shelter to help out. Mistaking it for a paid thing, she would ask Fluttershy what kind of documents she would have to have to come down there. After learning that there are none Sunset would go down on the weekend to help out.

At first, the person in charge at the shelter could be maybe an older woman who is pretty smart when it comes to humans and animals. She would of course be angry with Sunset as a first reaction, but sees something in her that makes her stop herself from just refusing Sunset's help. She keeps a close eye on Sunset through the security cameras as well as frequent checkups. Be it intuition or whatever, she knocks a mostly wrapped sub with only the end open and a couple bites missing off her desk when Sunset is in her office and into the trash.

Complaining that she would have to take the trash out to the dumpster to keep ants out of her office, Sunset quickly offers to take it out. Agreeing to let her, Sunset makes a pitstop at the lockers where she was allowed to hangup her jacket and stashed the sub in therebefore taking the rest out to the dumpster. Seeing this confirms part of the director's suspicions and at the end of the day Sunset asks about her pay and Fluttershy explains that it is volunteer work making Sunset upset, both angry and sad that her hopeful job and income to find a place to live and buy food vanished. The director tells Sunset that she would pay her for today since it was her fault for not making things clear with Sunset and tells her to give her a few minutes and get her things together to go home before telling Fluttershy to stay.

After showing Fluttershy the security footage and telling her the theories that Sunset comes from an abusive home, she agrees with the director that it was possible. That Sunset did display some signs of that at school. Calling Sunset back into the office the two grill her and finally drag it out that Sunset doesn't have parents or a home and yes she did keep the partially eaten sub from the trash. The director would take Sunset in and over the course of the next few weeks Sunset would mellow out as the older woman shows that she truly cares for Sunset and the two teens actually start to become friends.

From there there would be all kinds of ways this could go. Sunset could just forget the portal and admit to everyone that she messed up and end there as the sirens would have no reason to come to CHS as there was no light show to attract them. Or Sunset could confide in Fluttershy who would try and talk her out of it but Sunset still steals the crown and does mostly the same stuff trying to prove a point to Celestia except she would be nicer to Fluttershy.

So, good story idea or not? And where would you take it from here? By the end of the story Sunset would become a better person and possibly a real hero depending on what happens.

Interesting idea

If I wasn't so busy and had stories of my own to write I would totally take on this idea.