Dealing with Anticipatory Grief for Years

my mom got sick when I was 8 with thyroid cancer, she’s now on palliative care because a lot of other conditions have popped up since her cancer diagnosis. She’s been in remission from the cancer since 2012. Well I just got the news that there is a HIGH probability she has lung cancer since her last scans showed masses on her lungs and with the previous cancer they think it spread to her lungs. When I was a sophomore in HS (2016-17) they told us she had 6months-2years to live. When we got that news I went through the grieving process, my social worker called it “pre-grieving” but the actual term is anticipatory grief. So I had accepted the fact that my mom was going to die by the time I left high school. Well it’s now been 5 years and she is still alive. It is very hard for me to deal with her still being alive because part of my brain still sees her as being gone. With this new possible lung cancer diagnosis she would be considered terminal since she can not go through treatment or surgery due to her other conditions. My brain is having a very hard time coping with the fact that she may actually die soon. It’s so hard grieving someone who ended up living and then a few years later they say she is gonna die. I have no idea how I’m going to react to her actual death since I previously did that. I don’t know if any of this makes sense but I just needed to vent