Disney Fantasy has two more private spots with great views that you might be able to use if you get in touch with them.
I just got off Fantasy and saw a couple events at The Outlook on Deck 14. I talked with a crew member about the toddler play time they scheduled there and he said it does not get used much... mostly just for special events like weddings or family celebrat ions and such. You might be able to get it decorated just right... have some champagne and treats ready... and surprise her when you bring her up there to propose from the highest view.
I also see they have a Meridian Patio for special occasions. This may be an option, too, although I did not see it myself.
If you get in contact with
DCL I bet they would work with you on this since these spots are not used much. I was told The Outlook was empty the vast majority of the voyage.
A link to some info about them on the DCL weddings page:
https://www.disneyweddings.com