Believe it or not I think clay will work to Maria's benefit for once.
Anna doesn't move as well on clay. Her strokes are less effective because she relies on robbing opponents of time by taking the ball early and hitting flat. She can't hit heavy topspin balls to push Maria back, and she doesn't have Schnyder's (very impressive) serve.
I think this will be a straight sets win for Maria, who will be driving her forehand to all corners and having her way. And if it is close, Maria will still win.