I don't understand the idea that Sturgeon is bluffing, and May is calling her bluff. First, that would mean that Sturgeon doesn't want Indyref2 and is pretending - that sounds very unlikely to me. Second, to call her bluff, May would surely say, OK, let's have one now, when it would probably lose.
I'm sure there is an element of game playing going on, but I also think that Sturgeon is serious about Indyref2. As to May's position, I don't know, perhaps she wants to string it along, hoping it will fade away, or that Brexit will be very successful, so independence seems less attractive.