I leave the cycling side of it to my boyfriend :/ I might put her in the net and buy a hospital tank tomorrowHi and welcome to FishLore!
Unfortunately, I think it may be an issue of overcrowding still. The mollies and kribs should be in a bigger tank really, and may be getting aggressive before of territorial issues.
How long has your tank been set up?
How did you cycle it?
What are your current water parameters?
Your platy's fins are clamped, which definitely shows she is stressed, and moving her into the breeder box may stress her out. If you have a quarantine/hospital tank I would move her into there for now.