Can Vilemaw get Fortified Position shield after Vi's attack trigger?

The battlefield triggers when combat starts, at the same time as Vi's When I attack. Vi goes on the chain first, then the battlefield, then you choose targets. Only then do you get a reaction window. By then you already chose a Fortified Position target, so Vilemaw cannot get Shield in this scenario unless a move trigger let you play Vilemaw before combat starts.