You can either go into 4D off 5B/5C, or off jab pressure. Always be ready for it off a 5C. I would say weaker players will generally do it off of 5B/5C and better players off jabs however, since if you do 4D off a jab, that's also an anti-grab setup, and it's less predictable.
Also, watch Litchi's spacing whenever she uses 4D. It's -5, but because it has so many active frames, it can be up to +4.