It is up to you if you want to get another rabbit. Rabbits ARE social, but she will do just fine alone. However, you will have to make a point of spending good time with her.
I have actually heard that a lot of people think that two bunnies are better than one, because they keep each other company, but it is also true that you will have the expense of another rsbbit’s food and vet care.
If you do decide to get Cinnabun a friend, there are lots of amazing rabbits at shelters!

I certainly depends on the rabbit’s personality, but some do really enjoy having a friend. If you’re okay with the added expense and you aren’t too picky about who that new bunny is, then why not? I didn’t see if you said she was spayed yet or not. If not, that would need to be done first. Then you could take her to a shelter and let her pick out a friend for herself. That would make the best match.

Have you decided whether another dog will someday find a home with you again? Cinna may be perfectly happy alone with you, or with another dog as a friend. We recently lost our Sheba who was almost 15 yrs old to cancer, but Bumpy was still very new and hadn’t tried interacting with her. I understand the need to provide Fleur with a stress-free environment and am sorry that she’s ill. I wonder if Cinna will miss Fleur? She may need you as much as you may need her when Fleur is gone.