Card usage for abilities are determined from RIGHT to LEFT. Debuffs and Silver attack cards are the only exception to the clause. Debuffs have the highest priority which is why we use Blue Guila for our main damage and silver attack cards take priority over bronze attack cards.
Ultimate usage are determined from LEFT to RIGHT positioning. This means that the way we place units matter. Guila is to the left most side to ensure that she always gets her ultimate off before Howzer. The threshold for her 1 shot ultimate is a lot less than Howzer. There’s also a high chance that she’ll get a random combine early on which will guarantee her ultimate in turn 3.