My first instinct is to raise to protect our hand. Calling gives UTG 12:1 to call, which is great for her if she has 3.5 outs or more. My point is that she doesn't need much to profitably call this bet. She can call with any pair. However, raising gives her 7:1, which cuts her odds significantly. I think you have to 3-bet if you can't fold. MP2 could really be raising anything here, including Kx, Qx, Tx, Jx, A9 or any 2 diamonds, along with some other hands we wouldn't expect.