How would you say" She would have been thinking of her son." This was not accepted by DL.
"Lei" si può usare per rivolgersi a una seconda persona, vero? Poi, "You would have thought of your son" dovrebbe essere una traduzione corretta, no?
Not if you saw it in writing. In writing, anything relating to the formal "Lei" is capitalized. So it would have been "Suo figlio", not "suo figlio".
DL doesn't care about your capitalization, but their sentences are very consistent on that point.