I just looked it up myself, and you're right it was Lee. I could have sworn he hadn't taken over yet and it was still Silvestri, but I was clearly mistaken. That was issue #256, and was drawn by Lee. You are correct.
The issues where they foreshadowed her desire to become a warrior, however, were quite a ways prior and were long before Lee, of that much there's no doubt. Perhaps the seed of the idea for her transformation was planted then and Lee later helped finalize the design? It'd be interesting to find out who had what influence in the creative process that led to the asian Psylocke we now know.