Again, pardon me for being persistent but doesn't the Queen always have to follow the advice of her PM? What if May simply goes to the Queen and says "I request that your majesty dissolve parliament"?
We went through this in Canada. In 2006 the Harper Conservatives passed the "fixed elections act" stating that elections were to be every four years unless parliament voted no confidence in a minority government. In August 2008 Harper decided that he wanted to call a snap early election to try to get a majority. He simply went to the Governor General and requested a dissolution and he got it! The courts subsequently ruled that the Fixed Term law was only symbolic and that nothing could stand in the way of a PM being the only person who could give advice to the crown. Why would it be any different in the UK? The crown is the crown!
The UK Act does not explicitly abolish any extant prerogative powers of the Crown to dissolve Parliament and call a general election. It does impose a comprehensive scheme of when a general election can take place and deletes the previous statute law about the topic.
There may be room for legal argument, but I would interpret the present UK law as excluding a dissolution outside its terms.