McArdle handed debuts to Linfield defender Jane McMaster, Sparta Prague forward Kess Elmore, who made a lively appearance off the bench, and 16-year-old Cliftonville midfielder Charlotte Havern.
Aside from striker Cora Chambers, who was sent off in the closing stages of the loss on Friday, Northern Ireland have a full compliment of players to pick from for the second leg.
Telma Encarnacao scored an early opener in Larne before before Jessica Silva doubled the lead and Rebecca Holloway scored an own goal inside the opening half hour.
Northern Ireland improved after the restart, and looked the better side after Catarina Amado’s red card, but could not find a goal their pressure deserved, and the visitors capitalised as Fatima Pinto scored a speculative, long-range fourth.
McArdle knows where his side need to improve heading into the second leg.
He pointed to how Portugal were able to exploit the gaps between the centre-backs and the inexperienced full-back duo of McMaster and 19-year-old Emily Cassap, and how his own team could not convert their pressure into goals.
“The immediate reflection was misfortune with the scoreline, and how it was a bit harsh,” he said.
“Reflection-wise we still feel that way, however there’s areas that we need to improve upon before the game.
“There were some positives but obviously the scoreline is the scoreline.”
