I went back to one of the Diva website accounts to see what they actually claimed, and found this in the replies to the Intouch "article" by Jessica Pimentel (Maria Ruiz).

This is complete garbage and a lie. I am on this show. Kate is a professional in every way and has been around longer than anyone on the cast and it shows. She gets and earns my complete respect. Watching her work is a master class each day.
Is she real or fake? The comment is on the 5/7/14 page of her linked facebook account.
She's just one person.
Would you place a bet in Vegas on those odds?
You did.
You are betting that Kate is a "
word that rhymes with rich" based on
one annonymous report to a gossip website about OitNB.
If this Jessica Pimentel
is "real" ( I trust little when it comes to the internet) then this "one" woman is someone who is actually
on the set and works
not only with Kate but with a multitude of other women who work with Kate.
In past interviews the one thing that came through repeatedly from many different actresses was how well everyone gets along and how little diva-ness was being exhibited on the set.
As Teacake mentioned on page 1, these women go out together. Several have vacationed together, they celebrate birthdays together and even holidays.
As I pointed out, Kate hosted several costars at her home this past Thanksgiving and Danielle even bemoaned the fact that family obligations kept her from also attending.
Is there "someone" on the set who doesn't like Kate?
Quite possibly.
But that doesn't automatically make her a "diva".
It does automatically make me wonder about the level of self esteem from Mr/Ms Annonymous.
I've seen it in my own profession, coworkers who decry what they seem to believe is
diva behaviour while I thought it was just superior skills/understanding. I look at those "superior" coworkers as someone I can learn from, someone who WILL make me better, not as someone who "is" better.
Jessica Pimentel certainly seems to indicate that in her praise of the "Master class" she feels Mulgrew is conducting.