Hi Lourelle ~ welcome.
It's a fact of life that sisters squabble and daughters rebel against their mothers.
But I'll just make a few comments in response to what I have read.
Your Mum went away to work. You may well have felt abandoned and you might still resent her for this. Now that she has returned, you may feel that she has given up the right to tell you what to do.
But consider ~ why did she go away to work?
Was it to earn money to help raise you and your sister?
As a mother, I know that this would be a lot to cope with ~ not seeing your little ones grow up ~ and then having them resent you when you return.
If you don't see your father, either, that may make matters worse.
Now that you have your Mum back, try to build bridges, so that you may develop a good relationship.
If there is a disagreement, try to be objective as you explain yourself.
If you are ill with an ulcer, then this will affect your food needs and your mood, too. Perhaps your family needs to understand this better.
On the occasion that you describe, if your attitude to your mother was negative, then her response may have been negative, too. Parents are only human ~ just grown-up kids. Sometimes their offspring find it hard to accept this.
Maybe you need to ask her to have a heart-to-heart with you, where you can discuss the things that have been missing in both
of your lives, and how you can get on better, so that you can make up for lost time and not waste the present opportunity that you actually do
have to be together.
It may not be easy, but I'm guessing that it would be worth it.