My Wife Delivered A Girl Baby On 24th Sept 2015

My wife delivered a girl baby on 24th Sept 2015 with C-Section done on 38th week. The baby weight is 2.5 Kg. We have one elder Daughter who is two years old and born with C-Section done for my wife. During last semester of second pregnancy she suffered a pain on stitches. After delivery My doctor informed that her muscles inside has became hard and were ruptured. My questions are
1. Why her muscles became hard reason for it
2 .With this medical condition can she travel to other city by air with 4 to 5 hrs journey in flight
3. With my baby of 15 - 20 days old can travel safely considering the oxygen level in flight and exposure to public places any chances she and my wife will get infections
4. Which is the safest minimum period she should wait to travel such a long distance. Is it better to avoid long travelling at least for few months.