These posts happen a lot, so it's time to put some steps into writing to help troubleshoot this.
If you try to play as the Siren and it is not working (her costume doesn't show, her items are missing, etc), then the quickest way to find out why is to follow these steps:

1) Find where steam saves your options.ini file. On Windows this defaults to "...\Documents\My Games\Binding of Isaac Repentance" but if it's not there you're on your own finding it. Try googling.
2) Open options.ini and change "EnableDebugConsole=0" to "EnableDebugConsole=1", save the file and close it (this will not disable achievements or break your game)
3) Start the game, begin a run as Siren, and press the ` key (backtick, same button as ~)

You'll see red text showing errors and which mod is causing those errors. If the error is showing as a problem in Siren code, post your error on this discussion and I'll look in the code at that line number and see what's going on.


Things to note:
- Mods can break other mods extremely easily, if someone else wrote something dumb there's nothing I can do to fix it here.
- The version of the mod you get by subscribing to the workshop is the _only_ version I'll support. People come to me with versions from other places, I don't even know how it got there so of course it won't have my fixes.
- I've gotten too many "it doesn't work" messages over the years while the mod was in perfect working condition. If you can't give any more details or follow these steps, sorry I can't help you.