https://www.deviantart.com/thebenalpha/art/My-Older-Pony-Saving-the-Capitaine-Thunder-Burst-850401825
As you can see, it is not in very good condition. She has drunk too much, and she is no longer able to assist Spitfire at the Wonderbolts.
After the death of this sister, she is not really the same.
Here's an old drawing that shows Thunder's condition when she lost that sister: Sisterless
https://www.deviantart.com/thebenalpha/art/Sisterless-816608617
If you want to see more of the project, here is the folder: https://www.deviantart.com/thebenalpha/gallery/74451249/project
Even if you find it hard to believe it, it pains me to have written this to my characters.