"Hepi is trying to stay strong but deep down inside she is finding it difficult," she said.
"She only just lost her husband a few years ago and now she has lost her son. It is very tough on her."
Jonah's wife Nadene and their two sons Dhyrelle and Brayley attending today's service.
All Blacks great Michael Jones has praised Nadene for allowing New Zealanders to pay their respects to the rugby legend at different memorial celebrations over the past two weeks.
Today's service is the third public memorial in Lomu's honour.
"It's [today's service] really to reflect who he was and what he meant to us and we really have to acknowledge Nadene," Jones told Newstalk ZB today.
"She's let the nation and the different communities in. I think if it was her decision she probably would have just wanted it small and done privately.
"But she's really shared someone who was dearly loved by New Zealanders and people around the world over a day like today, so that's why we feel really privileged and honoured."
Image 1 of 27: Nadene says goodbye to husband and father, ex All Black and rugby great, Jonah Lomu. Photo / Nick Reed
Malupo has been to each memorial service for the rugby legend said it was great to see so many people come to say their farewells.
"It has been really hard but with everything that has been happening you can tell he was really loved," she said.
"There have always been big turn outs at each ceremony."
The 30-year-old said she was very "proud" to be related to Lomu.
Jonah Lomu's Hafoka Lomu has travelled all the way from the United States to join the service.
"I came all the way from Denver, Colarado to be here together with all the people from New Zealand, all the relatives, to mourn his loss and show all our love and respect for him as a man. Not only that but as a fan and as a best friend of his," Hafoka said.
"I had to excuse time out from work to come all the way here to show the true feeling about him.
"We come together today with everybody, the whole world, to mourn his loss.
"He was a great man and a great ambassador to the game of rugby. He was a family man and he did a lot of great work even though he was out of rugby he still spent his time promoting the game. That's how much he loved the game of rugby."