The 20-year-old has been at the club since 2017, and has now agreed a new 18-month deal until Summer 2021.
Hay says the new contract has helped her achieve her ambition of signing as a professional.
Speaking to RangersTV, she said: “I am absolutely over the moon, it is been an ambition of mine from when I was young.
“As a player, I think it is a massive step because I have been at Rangers for a couple of seasons now and I have just tried to work so hard and to get an opportunity like this it is just something I had to grab with both hands and I am over the moon for myself.”
Hay spent around 10 months out injured, making her comeback last year and on her returned picked up the SWPL Player of the Month award.
She added: “The injury was tough, it look a long time to get back to full fitness so I just feel to get back in the team and continue to keep growing it has just been a massive step for me and I am really happy to see what is going to happen next.
With two new signings already confirmed as Demi Vance and Jenna Fife join the squad, Hay is looking forward to meeting everyone in pre-season.
She continued: “I can’t wait to see who is going to be here, it is going to be a big change but change good sometimes so I am really looking forward to it.
“I’d like to win the league to be honest, I think if we continue to work hard and put in the effort and work hard for each other and the coaching staff and the club as a whole I really think we can do it.”