Adrienn sending out pokemon only once in one turn

[Corso 165]

During the battle against Adrienn, Grassy Field, xe had Gardevoir and Mawile on xyr side of the field. My Salazzle uses Sludge Wave, changing the field into Corrosive Field and Gardevoir faints (Mawile, which mega evolved at the start of the turn, takes no damage). Then xe sends Whimsicott out, but Whimsicott takes damage from the field and faints before the turn starts; however Adrienn doesn't send another pokemon out, so Mega Mawile is alone for that turn. Then if I take it out xe sends xyr last two pokemon out (Florges and Togekiss), if I let it live xe sends Togekiss out.