The fundamental thing is that while the woman is in the yoga session, she should focus much of her attention on how she feels and the symptoms she may have, and in case she needs it because she does not feel well, she should determine if it is a position in itself that causes her some discomfort and suspend the yoga session. If you feel any discomfort in your pelvis or lower back, it's best to sit, lie down or stand (whichever is easier for you depending on the position you're in) until the symptoms pass.