That is very common!!!! PACE, the program we use deals with that issue. You might want to encourage her to call her local (pro life) crisis pregnancy center to see if they have a support group. What better way to punish yourself for the rest of your life, than to refuse to forgive yourself.
Without talking to your sister, I can’t really judge the situation. But in regards to her parenting, perhaps it could be she is so happy to actually have children “alive” that she can’t bring herself to discipline. To spank them, cause them to cry or cause them to become temporarily unhappy with her (as all children do when they are disciplined). She could also be punishing herself as a mother. Perhaps she thinks she is unworthy of her children born alive. Perhaps she feels unworthy of the loving respect an obedient child could give her. I have no idea really, but this is normal to some degree. Every situation and woman is different and this can get very complex.
You can do a search if you like, to help your sister find a support group if she is interested. We use PACE (Post Abortion Counseling and Education). There is also Project Rachel.