Okay I have a somewhat different take on this and I may be way off base.

Perhaps your T was trying to reassure you that your SI scars weren't that bad as a way of normalizing or even being hopeful for you. It sounds like if you had to rip your tights to show her your thighs, she might have been worried that they were going to be very severe and was happy that they weren't. I know when I was going through all the IVF stuff my T had a hard time with any SI. His thing was that if the doctors saw evidence that I was actively engaging in that sort of behavior that they may decide that I am not stable enough to go through IVF. It may seem unfair but in a way it was true. If someone is going through this very challenging process to try to have a child then it is in everyones best interest to make sure that the parents to be are healthy and stable. It is also less likely for the IVF procedure to be successful if the woman isn't physically(ED?) healthy and emotionally healthy. Stress is hard on the body and if someone is struggling that much with their day to day life that they need to SI, then adding in all of the treatments and then a possible pregnancy are going to be adding additional stress, which might be a problem.

Sorry, my point was that perhaps when she saw the SI scars they didn't look bad enough to cause the doctors to question your stability to go through the procedures.