Advice- Mother issues

Hi ladies I just need to vent right now! I am 25, married for 2 years, grad school, career... I'm an adult. I have a 13 year old brother who has a lot of serious mental health issues. He lives with my mom (and step dad) who also has mental health, as well as physical helath issues. I live an hour away from them (which she constantly reminds me of). My mother does not call to see how I am or just to chat. It is always to ask for help. Now, I don't mind helping but that is the only reason she calls. I am out of state right now, my husband was called to cover a job, and I on fall break (teacher) and she just emailed me saying she needs more help. That my brother is doing this and that. Should I feel guilty and compelled to help? Or continue to live my own life? I took a day off of work two weeks ago to help her after her hysterectomy. And I call all the time to make sure things are okay. I just don't know what the healthy response is because I grew up in an unhealthy household. Thanks for your input. Btw last time my mom and I talked she yelled at me for giving my opinion about something saying if she wants my opinion she will ask for it. I always get caught up with, well we should be christ-like, but should we be a doormat? Thanks ladies, totally lost right now