Why? If she keeps working on her serve and ROS she could dictate points and keep them short, with clever positioning she doesn't need to move that much. The only problem is that she seems injury-prone, but maybe she'll figure it out with good conditioning and scheduling.
Because she now has reached or stumbled onto this mindset that she can be successfully only on indoor carpet or court where effect of natural elements are greatly minimized: no wind, not too much sun, temperature just about right, court condition ideal.
I also believe her injury are partly due to lack of conditioning, and with body type, it hard to be competitive past age 26.
She kind of reminds me of Lindsey and Seles body type, toward the end of their career it was hard to play well in a 3rd set
Petra is blessed with incredible talents.
Easy power, great hands, she can change the direction of the ball w/o too much contortion of her body like others.
But to maximize this talent and reach her full potential, she is going to need her body to be healthy in a sustained length of time, not sporadically.
Else she will find herself in a situation, where she has great sarts in matches, but cannot finish off opponent because her body can respond to her good player instinct because of lack of conditioning. And this continues, frustration will soon set in and she will fade.
Last but not last, she need to learn how to play and win out of her comfort zone.
Great champions like Serena, Venus, Maria, Henin, Kim, Capriati were not always playing in ideal conditions, but they learn how to minimize or overcome those the negative effect of those condition to pull through difficult matches, especially against opponent they are supposed to beat.
It seems to me, Petra has all but written off the North American tour is only focusing her chance on European indoor hard court.
Yes, she asthmatic, but instead of letting herself being defined by the condition, she can possibly find ways to minimize their effect.
I would like to think there are sport physicians who can help her with that.
Sport medicine is so developed now, there should be a way.