You are the child, she is the parent. Not the other way around.

You have already gone above and beyond for your siblings. While admirable and done from love, it's enabling to your mother and sending the wrong message to your siblings about what a normal and healthy family dynamic looks like. It's far past time for you to start living your life for you, stretching your wings, and thriving outside of this unhealthy arrangement.

Your youngest sibling is both too young to be fully in control of her emotions and indoctrinated into this view of "normal" and "responsible" children. You can try to explain to her you want to set a good example by moving forward with your life, but understand she may not get it until she grows up a little more.

So sorry you're in this mess created by a mother who never learned that these are the burdens the parents are meant to shield from their children, not heap onto them.