My niece was 3 when my mom passed away. My niece knew my mom was sick and at the doctor’s (hospital). After my mom died, my niece didn’t want to go to the doctor or for any of the family to say they were going to the doctor. She thought we wouldn’t come home. With that back story, it’s really important to explain to your daughter that you don’t have a sore throat or an upset tummy that the doctor can fix but something else and the doctor can’t fix it. We told my niece that and said that my mom went to heaven and God could make her all better but that meant she couldn’t come home.
Oh and I agree with another post, write your daughter letters for birthdays and all the big events, high school graduation, college, first job, marriage, kids. And then write down your life stories, tell her about your childhood, growing up, things from being an adult, etc. so she can remember you and get to know you better as she gets older. Hope this helps!