I have to disagree. I wanted to leave the collar on, but had to take it off to progress the story.
I was pleasantly surprised that it still shows her as wearing it.
Put a different 'relationship' option in for those that don't want to remove the collar IMO.
Then you took it off... it's gone. Also, why did you HAVE to take it off? It's optional, isn't it?
And wait... you want to keep a shock collar on her but still have her be your girlfriend, am I reading that right?