The Mariners folded after the first two seasons but have returned for the upcoming campaign.
"Mariners being my first A-League club in the inaugural season, they've always held a special place in my heart and it's a real full circle moment for me," Simon said.
"The closer I came to this decision, the more it felt right for a number of reasons.
"Coming off a really difficult 10 or so months it was a priority of mine to be somewhere I felt supported and to be in an environment surrounded by the best medical care and resources."
Simon was contentiously selected in the Matildas' Women's World Cup squad despite not having played since tearing her left anterior cruciate ligament for former club Tottenham in October last year.
The striker did not play a single minute in her third World Cup.
"The versatility and quality Kyah possesses as a forward, who has experience in some of the best leagues in women's football, is an exciting signing for us," coach Emily Husband said.
"Her international career speaks for itself as she has scored in both the Olympic Games and World Cups.
"To bring that experience and proven ability to score in big moments to the Central Coast is excellent."
"I had a great experience during my first stint at the club ... and I'm looking forward to achieving more success this season," Gielnik said.
Coach Jeff Hopkins welcomed the return of the 54-cap international, who helped Victory to the 2018/19 premiership.
"It's wonderful to have a player of her calibre return to the league and join our squad for the upcoming season," he said.
The ALW gets underway on Saturday, October 14.