Jennifer Davy died last week on the eve of Thursday’s game at Leeds Rhinos which Huddersfield duly won with a surprise 31-12 success.
Speaking after the much-needed victory at Headingley, McGillvary, who represents his country against Samoa on Saturday, admitted: “That win was for the Davy family.
“Jennifer was very special; from when I was really young (on loan) at Batley, she took time out to come and watch me.
“She’s the reason Ken is a part of this club; she’s a local Huddersfield girl and she got Ken to invest in us – she’s been our No 1 fan and it’s been a real shock to us all.
“She only texted me three days ago congratulating me on the England call-up, and to then find out of her passing... something left my body.
“I couldn’t focus properly at all: but that win was for her,” he added.
It was Huddersfield’s first victory in 10 games as they look to revive their campaign.
“On Wednesday when we found out, we made a big point of making Ken and Jennifer proud by putting in a spirited performance,” continued McGillvary.
“They’ve been watching us under-perform in the last 18 months but stayed committed to us; they pay us on time, they come watch every match and Ken comes in and gives us really positive talks so we needed to pay the Davy family back with the effort, and I think we did that.”
Giants host league leaders Castleford Tigers on Thursday.
McGillvary, 28, admitted: “They are an awesome team, the best I’ve come across this year.
“Defensively with their line speed they’re amazing but we’re at home and it’s another chance to show our fighting spirit.
“I’ll be watching it early in the morning somewhere and wishing the boys good luck, but they can do it: I’m just one player in a big squad.
“If we can replicate this effort tonight we won’t be far off,” he added.