She can't make you feel anything unless you give her permission
The only way she can cope with the situation with your stepfather is to be in denial.
Think of a dysfunctional family unit as a baby mobile hanging over a crib. Each piece has its place (family role) and the mobile is perfectly balanced.
If a piece of that mobile (family member) is taken away (establishes boundaries, finds recovery, etc etc etc), the mobile goes all haywire, trying to get back into balance. trying to get that missing piece back.
There is absolutely nothing wrong with establishing healthy boundaries for you and your family.
Just be aware that the mobile will be thrown off balance, and it's up to you whether you want to pick up someone else's emotions or not.
I no longer feel guilty about establishing boundaries in my life/home, but it's taken a lot of practice over and over, and working past the discomfort of standing up for myself because that was a whole new behavior for me in recovery!
Make any sense?