I have no prob with MBR as an item. I honestly LOVE it. It's one of the best offensive items in the game, if not the best....
....the problem is that MBR costs so much and only gives you 30 AD for your Q and ult. Yes, MBR is applied on Q, but it adds NOTHING to your R, which is where a majority of your teamfight damage is coming from.
Not only that, but MBR is incredibly expensive. You can buy 2 BF swords for its cost and have some change left over. For that you'll have 70 more AD (than an MBR) and a lot more explosiveness.
Please buy black cleaver on her (for her Q). Please buy IE or BTs. Stack AD ffs. Just do it. It's the only offensive stat you need. This doesn't mean forget survivability, it just means AD should be your primary offensive stat.