I always feel for athletes or singers whenever they have an injury or a sickness. According to Ariana, she has a sinus infection and is really sick. Its been going on the last few weeks with her and it might be in her best interest just to stop the tour temporarily until she gets healthy. I would hate to be a fan that pays for tickets to one of her shows and doesn't get her at 100%.
I know she will do the right thing and whatever decision she makes the fans will be happy.