MIL comment

I'm having mixed feeling about a comment my MIL made.. she flew in today to stay with us for a week and she keeps saying her and my SIL couldn't believe I had it in me to give birth and be a mom 😐 and that they are so surprised I was "good" at delivering my baby because I had a pretty fast delivery. 
Idk why it bothers me so much she keeps saying it. Like wth do they think about me? Should I be offended? Would you be offended?