Sure, let's get to it then. Keep in mind that changing flags and variables like this has the potential to mess something up, so
back up your saves before attempting it in case something goes wrong.
First you're gonna have to enable the console, it's disabled by default. Look for the file "[your game folder]\renpy\common\00console.rpy", open it with a text editor (I use Notepad++) and look for the line that says "config.console = False"
Change it to "config.console = True", save it/close it then run the game.
Load up your save file, then press Shift + O. If everything went right, you'll see the console window over the game. The variable you want to change is called "hasniasupplies". If you type that in the console (without quotes) it'll tell you the current value, which will probably be False since you're having trouble triggering the event; type in "hasniasupplies = True" (again, no quotes) to change the value. Now in my testing, the event won't trigger on the same day by changing the flag like this, so go do something else for the day, and on the next day go visit her in the sanctuary and see if it worked.