Cindy, it is always hard to lose a friend, and to know she was not honoured correctly adds to that loss. You have my sympathy also. It is important to make arrangements for things that are important too you, and your advice is appreciated. For myself, I don't believe in an afterlife, so I won't be aware of what happens to me. My concerns would be primarily for my family. If it lessened their loss to misgender me at my funeral, I would be ok with it. We are all different, but you are absolutely right to remind us we need to look after this aspect of our life.
Oh, and I would add that if this is important to you, your age shouldn't matter as to when you make a will.
Allie