I love horizontal portraits, love tones of negative space, love framings etc. I've read enough of "horizontal portraits is not a proper portrait" kind of comments and when I posted the photo I just wasn't in a mood to listen more about that.
If that is all you are hearing, then you are missing something. That might be what other members have written to you and others, but apparently you have missed the reason that the comment was made.
In case you have never read that comment by me, I will try to explain: The times I usually object to "horizontal portraits" is when the photographer includes too much negative space on one or both sides of the subject,
for no apparent reason, while often at the same time cropping a portion of the subject's head, or cropping the body at an unusual place. In shots such as that, I will suggest that the photographer turn the camera. Or even shoot wide and crop to vertical later.
I have seen many portraits in horizontal format that are simply adorable, and it is usually because the photographer has framed the subject exquisitely with good balance to the overall composition. There is a thread here with that theme. Worth a look, if you have not seen it.
Your example here is not objectionable, and you have heard no objection from me in that regard. The only reason I did not nominate it for POTM (long before D-B-J did) was because there is something in front of her face.
So you see, it's not always automatically a bad thing to frame a headshot horizontally. BTW: the background is the thing that makes framing this in horizontal format make sense.
I hope that helps.