Sasori's puppet body was in actuality a very good defensive strategy, as his heart implant could be redirected to another puppet at will.
Sakura is a smart lady; without Chiyo, she could have figured out Sasori's shell's weakness, albeit with more time fighting it. However, we have to remember the part where Sasori unleashes those thousands of needle-like attacks that poisons all who touch it. She was using Chyo's chakra string to dodge the attacks. Then again, she did not know Sakura had antidotes to save her for five minutes each. That being said, the needles still puncture the body--enough punctures from the needles mean too much blood loss to handle. So where does Sakura come in at this point? She has healing jutsu, but it takes time for her to heal one injury point. These needles would puncture her in multiple areas. In the end, Sasori would win against Sakura with medium difficulty.