It is puzzling - at first seems Jennifer played extrimely well, and as result she lost. One can say Petrova played really well as well, but this is not good enough, Petrova is not even top player, and Jen should have that match. So now we going back to "school" to look for the reason(s).
Here is what I think. Yes, Jennifer needs to correct in a hurry her serve! Yes, she needs to get new coach, and it better be best one! (I wrote about need of the new coach last winter!!!!) To papa, yes, you can travel with Jen, but let somebody else to work with your girl.
Most of all, I think Jen is a little bit behind in her mental game. These days you can NOT play every match and adjust your level to the level of your opponent. And it is what Jen does every time! She needs to start playing her game, and start kicking most girls with 6-1, 6-0 victories, and play top dogs on her level, instead of giving them chance to dictate. Jennifer should stop just simply returning ball back, and start setup her points! This is not good enough just to bring balls back, your opponent will take advantage of that. Even Petrova made Jen run and chase balls, and had so many winners on the lines just because Jen would bring ball back right to the middle of the court!
Does anyone in Jennifer's gang is talking about mental state? Is anyone working with Jen on that??? Can anybody tell Jen that she is loosing all these matches just because she can not hold her serve?