Lamashtu with potion of irrelevance

[micmurph]

so first round of the game, Player 3 kicks in the door and is greeted by Lamashtu, reading the card, 2 other players wanted to add 2 monsters to the combat. Player 3 wanted to play Potion of Irrelevance on Lamashtu, to send it away, but since the card says, "When the monster "First Appears" any other player can add a monster to the fight. Player 3 argued that since he made Lamashtu run away, the added monsters shouldn't be added and he should win the combat. The other players argued that "First Appears" means that, the monster adding step happens before Player 3 is able to play his potion... so who is right?

[Andrew Hackard]

The other players get a chance to exercise the "first appears" clause, but they must do so immediately -- if they start to dither about whether they want to add a monster or not, the player fighting Lamashtu can send her away.