Stress is part of life, and as an adult, she should be able to deal with things. I don't know your wife or how she deals with changes in her life, but I wouldn't wait long at all. Going back to work will be followed by the stress of having to get up every day and going to work, and dealing with co workers could be stressful. A diabetic child while definitely serious is something that can and will be managed medically. It's part of being a parent.
I'm a firm believer in taking control of my life. Whatever your feelings are, they'll only get stronger over time. They do not go away. I would give a great deal of thought as to what I would like to do with my life. Do you intend on transitioning? Are you interested in HRT? What do YOU hope for in the future? Make your own decisions, and take it from there, or you'll never be happy.
I can easily understand your concern for your wife's feelings, but you aren't describing anything that should really leave her on the floor. She's a big girl.