Hmm, don't think you can redo the event by using a save editor. You can try doing it by using a console command.
To activate the console download the
Unren.bat to your LoSeSb directory, run it and select 3 to enable the console.
In game press Shift+O then type in
DONE.pop("lexi_sasha_1")
and press enter. Make sure to type it in exactly like that (or use CTRL+C and CTRL+V), because the function is case sensitive...
After that do the date with Lexi in the mall again when Sasha is working and the event should trigger. (Don't overwrite your old save until you're sure everything is working fine!)
(If you don't want the debugging messages on the screen open the game\unren-dev.rpy with a texteditor and remove the
config.developer = True
line or delete the unren-dev.rpy and unren-dev.rpyc entireley...)