The mare picked up a $200,000 bonus for her connections following Saturday's win after being balloted from Tuesday's Melbourne Cup.
Mullins, who first came to Australia to watch Vintage Crop win the Melbourne Cup in 1993, has been a regular carnival visitor in recent years with Max Dynamite giving the trainer with Cup placings in 2015 and 2016.
OTI Racing took a part lease of the mare to bring her to Melbourne with the hope of running in the Cup.
"We're happy, we have a winner," Mullins said.
"A winner is also better than finishing fifth or sixth in the Cup."
Mullins indicated True Self may now head to the Hong Kong Vase at Sha Tin in December.
After beginning her career as a jumper, True Self has made a successful transition to flat racing.
"It's extraordinary," Mullins said.
"My son and Paul Byrne bought her out of a bumper in England.
"She arrived home in the yard and they told me they'd bought a jumping mare and I said 'I hope you don't own that', but here she is, she's brought us down here and provided us with a win.
"I never dream't she'd be a flat mare, I don't think anyone did."
While Mullins has no concerns with True Self's stamina because the mare is a winner over 4000m in a hurdle race, the trainer said he has differing views from jockeys who ride her on the flat.
"A lot of the flat jockeys that ride her say she has a lot of speed," Mullins said.
"Ryan is thinking of coming back in trip while I'm thinking of coming out for the Melbourne Cup next year."