There is no advantage other than hiding the info from the public.
If she has quit then she may just want it hidden, but is unsure if she will be back or not.
I think it's quite literally just a preference for some to hide from view, or to keep it open if they have quit. I would assume by hiding it if she has photos and videos for sale, it would be less of an advantage having the password on because people who are missing her can't go and buy her content. I have done this with a model who hasn't been on for years, I bought one of her videos - for nostalgia purpose because she was great and I really enjoyed her.
But it's quite simply a case of "each to their own" I think for this
I think some Studios hide it so they can delete all the current models content and then they can let another model work from that same account