Even though she didn't have a great year in 2012 Barthel played very good indoor in the last 2 years. In 2011 she won 27 matches indoor and she lost just 2 sets. This year she reached the quarterfinals at Paris where she lost to Wickmayer after 3 close sets. She also reached quarterfinals at Copenhagen where she lost to Kerber in 3 sets.
Watson's best performance last year was a final at Shrewsbury against Barthel. Mona won that final in 2 sets: 60/63. This year she played just one match indoors against Sofia Ardvidsson. She lost 62/63 and Ardvidsson eventually won that Memphis Open.
Even though Barthel didn't played that good in 2012 i think that she can win this match in 2 sets because she's a different player when she plays indoors with no wind and a constant temperature. Watson has good footwork and sometimes you need to play an extra shot to win the point but Barthel likes to hit hard the ball and that might be a problem for the young english player.