Hugs to you Chicory.
No, what you grandma did was not enabling. She did the right thing to love and care for you and your sisters at a time when your mother could not. Imagine if she had not stepped in.
You felt an extra load to bear as the oldest. I grew up the oldest of eight natural, step, and adopted siblings with my mom and stepdad in a very loving home, after AF left my mom with four daughters. Caretaking is what we do by default. Some of us may already have naturally giving, loving, caring personalities. IMO, it is often the unhealthy circumstances in our young lives that later cause us to choose or foster unhealthy relationships...that eventually cause us to develop our codependent traits.
Keep sharing with us. I think you're doing amazing things right now.