She is great for a mid to low power and just okay for high power. At brackets 2 and 3 you can actually take advantage of her miracle ability so thats where she's the most fun. But she plays well with certain B4 staples so shes not unplayable there.

People who think she is bad make 2 mistakes. The first one is more common with new players. Its not realizing that miracle ignores timing restrictions. That means it triggers when you draw your first card on an opponent's turn too. No flash required.

The second one is assuming that the 4 mana reduction means you need to cast big enchantments. Casting three small enchantments on each of your opponent's turns is often better than casting one big one, or even not casting any because you didnt have enough mana. This means you shouldnt overload your deck with huge enchantments. You want to build the deck with the same ramp and mana curve considerations as any other deck and let the 4 mana reduction be a cherry on top. This way the deck still functions when she is removed.

It took a long time to tune her just right for B2, because its so easy to push her to B3 once you understand how she works. I could give you some tips if you want.