The pair struck up a close friendship during their time together at Mercedes, with Cullen playing an important role as Hamilton added four more world titles to his haul.
Despite their professional relationship coming to a surprise end last year, they have remained close, with Hamilton keeping a close eye on her latest adventure stateside in the world of IndyCar racing.
Cullen labels California track 'incredible'
Cullen now works alongside fellow New Zealander and Chip Ganassi Racing driver Marcus Armstrong.
The compatriots have forged up a strong connection in recent months, with Armstrong hailing her impact despite the 24-year-old experiencing an up-and-down campaign so far.
Though enduring some difficult times on the track, Cullen is enjoying her role, and getting the opportunity to live new experiences.
Speaking on the IndyCar YouTube channel at this season's Firestone Grand Prix of Monterey - held at Laguna Seca in California - the 50-year-old admitted she was left stunned after seeing the legendary circuit up-close.
“I’ve been here four days - but first impression, it’s incredible!” she explained.
“So, I was running on the beach this morning - it’s Monterey, it’s really close to the coast, so there’s so much here to do. You get that energy from the sea, we’re between San Francisco and LA.
“When you drive out here, you drive up this crazy hill, you come up over the peak and you see the track and you’re like, are you serious?”
When asked about the world-renowned corkscrew, Cullen replied: “Oh my god! Seriously, just look at this! It’s crazy! I mean, you can just see how physical this must be when they’re coming in with speed. Tucking into that corner and getting around there - it’s insane.”