Her first was vintage Duckling - audaciously lobbing the visiting keeper midway through the first half to give Middlesbrough the lead. Duckling doubled the lead 15 minutes later after springing the offside trap to go round the 'keeper and at 2-0, the hosts looked in charge.
But Claire Helm put through her own net on the hour mark to give Darlington hope and then Claire Armstrong found space to equalise in the 73rd minute. But just when the visitors thought they had salvaged something, Duckling smashed home the winner five minutes later to fire Middlesbrough into the next round.
Club Secretary Trevor Wing said: "Nicky is a fantastic player and really took her goals well. She was brilliant today and I'm delighted to be in the next round.
"Darlington pushed us all the way but Nicky's goals saw us through."
Joining them in the hat for the Third Round will be Chesham United, but they did it the hard way after they beat Havant and Waterlooville 2-0. After Alex Rodgers had given the visitors the lead after one minute and Anneka Nuttal doubled the lead, it looked as if Havant were in for a drubbing.
But Sian Williams saw red for the visitors who then had to withstand a barrage of attacks. But Chesham's defence stood firm to knock out the Hampshire side.
Williams said: "By the letter of the law, I was the last player so I guess I should have gone. I was a bit unlucky but it doesn't matter because the main thing is we won. The players were excellent and showed great team spirit."
Elsewhere, York City needed an extra half hour to beat Liverpool Feds LFC 2-1 after Genna Perischine had given the visitors the lead. But City fought back well as Jasmine Fillingham equalised after 25 minutes and Ruth Brazier netted after 100 minutes to win it in extra-time.