I have no depth to my knowledge in this area. One time years ago a guy showed me how to graft fruit tree rootstocks and scions, and we did that for an afternoon, so I had some concepts I recycled when pot plants split. When I've made repairs where branches split from the trunk, I've used what I had on hand, which has usually been electrical tape. The few times it's happened have been later in the grow, so I've just left the tape on for the duration.
I don't know with an annual if the way they mend would build enough tensile strength in the bond to hold up both halves of that plant when in the full weight of flowering. So personally, I think I'd leave it wrapped for as long as possible. One thing that occurs to me is the zip ties will bind as the trunk grows thicker, so you might need to replace them with something rubber-based or similarly flexible that can support it but also expand over time. Just ideas, I've got no real training with this. I hope she makes it!