I am so sorry you are walking the path you are right now, and my heart goes out to you.
The only thing I can think of that's more difficult regarding making funeral plans now is making them afterward, when you will be in such a whirl of emotion, possibly having difficulty making any decisions at all.
My own mother made her arrangements well before she passed, and she had me come with her to the funeral home. I remember her sitting calmly in the office doing this business while I paced, and even started walking out the door for some fresh air. It was almost too much. Then her voice: "M, get back here and sit down." I smile as I write this because she said it as to a young child, but ever so lovingly, and she knew I needed to be there to hear and witness what was being done.
She was so strong for me. She looked out for me until her last breath.
So, tough as it is, I say to go ahead and do it now. You are in a better frame of mind now (yes, really) to decide what you would like, and will be able to create a service with all the things that pay tribute to her life.
I wish you well.
Maggie