Broken Promises: Dealing with a Parent Who Doesn't Keep Their Word

No you're not overthinking. I've experienced similar situations where people have been unempathetic and continue to be unapologetic for their hurtful behaviors. Have you tried to express to your mom how it makes you feel when she breaks promises and then keeps doing the same behaviors? Pointing out specific situations and starting a discussion with her could be a way to then set better boundaries for your relationship moving forward