As someone who has almost never shaved, far more than "this is a big turn off for me" or "this is unhygenic", the response I've gotten is "this makes you [and by extension us] look bad in front of other people." (And the few times I have shaved have been in response to that - i.e., for someone else's event where I'd be highly visible.) There could be other reasons too - there are even phobias about it, or LW could be seeing it as a symbol of other things they don't want to acquiesce to, or LW doesn't like her reasoning for doing it.

My advice is going to be different depending on why LW "has a problem with it now".

But LW has made no attempt in the letter to articulate why they object so I would suggest the first thing they do is figure that out and then sit with it for awhile and decide if those reasons are an LW problem, a both of them problem, or an "I'm willing to break up over this" problem, and then act accordingly.