That rumor has been floating around the internet for a great deal of time, and has been debunked repeatedly. From what I understand, the show turned out approximately how she intended it to; a slice-of-life series with occasional adventures. Some episode pitches were shot down, but that's to be expected. Hasbro played no part in this. In truth, she retired from the team because of how difficult it had been to supervise the episode production.
She lives in Los Angeles, while the main voice acting and animation studios reside in Canada. She was managing most of the episode direction via phone, which, no-doubt, isn't the most efficient system. As the show expanded, her total control over it diminished, so she did what she felt necessary and stepped down.
While the situation could have been handled differently, keep in mind, her inability to keep up with production wasn't the only aspect that contributed to her decision. Her schedule is vast. MLP:FiM wasn't the only project she was involved in at the time, and juggling it alongside other projects must have been stressful. She didn't quit due to conflicting views, monitoring MLP simply became too difficult.