Had this exact situation happen to me with the grandma of one of my IRL friends last year (his family was always very supportive, thoughtful and kind to me, so her death hurt me in a way) and currently with my grandpa, who while not having dementia or anything like that, he has a sort of cancer and can't even go to the bathroom recently. We basically take turns between my mother and I, my Aunt and my uncle to go the entire week to take care of him.
Honestly MightyP, death is a complex matter, people handle It in extremely different ways. I personally, am not someone who goes to the funerals of close family members because of my inability to cry, so the way I handle It is by spending some time on my own, and get myself to relax and prepare myself to support in any way my other family members. I do go to the funerals of people unrelated to my family, since I can hide my inability to cry easier and people usually want me to be there so I can emotionally support them and help them distract themselves a little.
So yeah, if you were to ask me on personal experience, I would try my best to be there for your family members. It is gonna be tough, specially because she was someone really close to you, but trust me when I say that if your family really loves you, they will deeply appreciate just the fact you are spending time near them and giving all the support you genuiely can to make sure ya'll get through this.
Whatever happens, just know that you can count on me or
Noipoi
if you ever need anything. Both of us would love to help you in any shape or form.