For anyone else on Linux that gets the error:

Default Audio Player for mp3 files is not set up, like vlc or something.

when you try to run it, note that Stephanie depends on the python module os.startfile[0] which apparently is a Windows only thing that works like xdg-open. I'm not a python expert but here's what I did: the offending file is stephanie-va-master/Stephanie/TextManager/speaker.py. If you edit line 15 which is:

os.startfile(self.speak_result)

and change it to:

os.system("xdg-open " + self.speak_result)

everything works. Somebody else more knowledgeable can probably suggest something better.

[0]https://docs.python.org/3.6/library/os.html#os.startfile

Edit: Fixed! They fixed it by wrapping that line in an if statement checking the output of sys.platform. Very responsive dev.