Until which shloka can ladies recite Vishnu Sahasranamam? As I have had this lingering doubt for a long time, I recited only the phala shruti until now.

As per the traditions of old, ladies do not recite Sri Vishnu Sahasranam.
The reason is not clear as to the recitation of phala shruti alone, because phala shruti lists out the benefits of reciting a Stotram. Without recitation of Stotram, no meaning in reciting phala shruti alone.