The problem was that the rest of the world probably wouldn't listen. Even if she hadn't unintentionally done her best to alienate Equestria's neighbours, many of them would still see a rogue alicorn as a pony problem, and therefore a problem for ponies to fix. Even the more far flung pony nations like Saddle Arabia and Mustangia would likely say so because they don't have alicorns, and don't understand the threat one like Faust poses. Equestria could very well face this crisis on its own.