It's not surprising she lost to Garbin. Garbin is a tough clay courter if you are not on top of your game. JHH is someone who needs match play to get in form, and Clijsters is the same way. It is just too bad for WTA when JHH, Clisters, Serena, and Venus can not be healthy at the same time.
So far this year at French, it seems those who didn't play much on clay before French don't do well. I am not sure about Serena's chance at the French this year. This is probably the best chance for Mauresmo to win at French. Mauresmo matches up better against Venus and Jennifer than against Serena. I am not sure about Serena's form so far. Her play since her comeback has been more lackluster than I expected. I expected her to comeback to her old form more quickly than she has been since she didn't need as many matches play as JHH. I would pick Serena if she can come out of against Jennifer, Venus; otherwise, I would pick Mauresmo.