This reads a lot like an attack. Yes its clear they did not program their app 100% themselves. I fail to see how it's such a big deal. Especially one that requires posts on multiple platforms targeting her. The other developers seem happy for her to take the credit, presumably as its good for marketing. Who is this really hurting?
When someone very prominently says they made an app, someone else says they didn't and the first person responds with calling them jobless, disturbed and a harasser then the gloves are off. And it hardly reads like an attack to me anyway, there are no insults, no ill wishes to her career or life, it's just very firm.
Well that reaction seems to have come after they were harrassed, called a dumb kid, and a lying piece of shit[1]. This is a 16 year old, they're going to make mistakes. This level of hate for something very minor is really out of proportion.
They did after all contribute at least partly towards the app, so it's more of an exaggeration than an all out lie.