Its hard to see what the German angle is here; maybe there is something coming down the EU line and she is thinking ahead? The announcement is too public to be a manoeuver, it will be embarrassing to pull back.
I was once a Merkel fan, but have learned not to trust her. She is Machiavellian; saw this on her visit to the UK a few years back - made all these public speeches with Cameron about supporting the British claims of a need to change the EU conditions, and on who Germany would back in the leadership run - and then went to France and said the exact opposite and poo-pooed what she claimed in the UK - and openly backed the person she said she wouldn't. I understand that she should not be at the beck and call of the UK - not saying that she should - but being intentionally duplicitous makes me trust her not at all!