I also used to have so much fear, anxiety, and over all uneasy feelings...especially when something seemed good. Good things rarely seemed to happen and when it did I didn't want it to end.
However, we can't control people or outcomes. Your mom may or may not relapse. Either way it's out of your control. Enjoy her sobriety today and let go of the future you have no control of. Give your fears to whoever or whatever your higher power is.
You will be ok regardless of the choices your mom makes.
A motto I live by is that my happiness and self worth is dependent on no one. I have to give that to myself.