From Chancellor Merkel's POV, if you don't win a crucial state election you shall not give momentum to your political adversaries. If YOU wanted to take the reins and keep them there you have to reconsider all your options, well, on short notice, too.  

Chancellor Merkel is most popular than ever. She needs to keep her own momentum und thrust. Don't make your opponent look favorably. At present Peer Steinbrueck, as front-runner for the SPD and candidate for a take-over by a "Red-Green"-coalition, has been pissing off voters by his "greed remarks" of being really underpaid as Chancellor for the Federal Republic in comparision to some CEOs of public saving and loans banks in big German cities.  

Why shouldn't Angie make the surprise by calling "snap elections"?

#1 She doesn't need much preparation for this, and the election campaign for national elections prior to Easter would only last few weeks instead of months of dancing on raw eggs with her coalition partner.

#2 She really can make points versus her opponent Steinbrueck. By keeping pressure on him, she will be able to show and maintain his "greedy attitude" instead of making him mummy's and daddy's darling.

#3 She would have more options now than in fall. "Snap election" as surprise remedy would also keep emerging parties out, like the "Pirates". With five party colors in parliament (BLACK for conservative CDU/CSU, RED for SPD, GREEN for Greens, YELLOW for FDP and dark red for the SED/PDS socialist "The Leftists"), it's quite likely that RED-GREEN wouldn't have an edge now. So Angie has more to choose from:

"BLACK-YELLOW" as her favorite combination

or even a Jamaica-coalition of BLACK-GREEN-YELLOW

or a grand-coalition BLACK-RED without Steinbrueck who might then return to more income prospects by making private speeches for 15.000 euros each.

The state election of Lower Saxony has shown that the FreeDems are going to stay well above the 5 percent qualification hurdle by borrowing votes from the conservative electorate. This Pro-Angie momentum could be fading by fall, and tactical maneuvering might not pay off.

Will Angie play the quasi-risky game? Hopefully, else she is doomed when Peer Steinbrueck promises the heaven and becomes mom's and dad's favorite.

Angela Merkel is strong enough to tackle EU's and Euro's problems and make an election campaign simultaneously. She is able for multi-tasking.

The catch for making snap election possible is that she has to lose a vote of confidence in the lower house of parliament, not a big deal - has happened multiple times before with different chancellors.

In the case of losing a vote of confidence, the Federal President Joachim Gauck may dissolve parliament and call for early elections.

That would only be a minor stain on her blouse in order to stay in office for the next four years to come.