I dunno, there could be so many reasons why she is gone, she obviously had a bee in her bonnet about instagram for a while before she went silent, sometimes people just can’t hack it anymore.
I used to have an account that had a fairly sizeable following (not quite as much as Joanna) and I did the same, just deactivated my account one day because I was fed up of it, the pressure of posting, making every meal or picture look Instagramable and worrying when you didn’t get the number of likes that made you feel popular, maybe she just realises she is not the influencer she longs to be...
Of course I could be wrong and there could be another reason she has gone.
But I checked on Facebook and they are still together as per that