Ruddy (pictured above) hopes the team can replicate the performance in 2019 and reached the Finals of the UEFA Women's Under-19 European Championship in Scotland.
"It would be amazing to qualify for Scotland. All of the girls are focused on that. We were such a tight group at Under-17 level and we had a real good buzz about the squad. We have that again this year. If we win tomorrow, it sets us up well for the Spanish game."
Ruddy started all three games in the Qualifying Round, scoring two goals, and started in last Wednesday's Elite Round win over Hungary.
The Kildare midfielder hopes that the experience of playing in last year's Elite Round in Cork can help the team this year, with the newcomers to the squad.
"Because I'm one of the senior players, I have more of a responsibility. It's a team effort though. We all have something to offer to the team," she said.
"Winning the Hungary game was key. Last year, we didn't get off to a great start and it set the tone. Everyone is buzzing here after the 4-0 win. We're all set for the next two games."
Ruddy is studying in the United States in Central Connecticut State University, and the standard of football Stateside has seen the midfielder improve her all-round game.
"The game is fast. I'm playing girls that are four-years older than me. It's brought me on physically. I'm stronger now that I ever was," she stated.
Serbia lost their opening Elite Round match 2-0 to Spain and Ruddy expects a tough test on Saturday.
"We played them at Under-17s two years ago in the Elite Round. It was a battle. They look very organised, but we have our own plans ready to counter-act what they'll do."
Head Coach Dave Connell confirmed that there is a clean bill of health in the squad with all 20 players in contention for selection.
The team return to action on Saturday afternoon at 12pm Irish time against Serbia.
Republic of Ireland Women's Under-19 squad
Goalkeepers: Erica Turner (DLR Waves), Rachael Kelly (Shelbourne)
Defenders: Sadhbh Doyle (Galway WFC), Roisin McGovern (DLR Waves), Rachel Baynes (Galway WFC), Aoife Slattery (Wexford Youths), Leah Brady (Galway WFC), Katie Burdis (DLR Waves)
Midfielders: Lucia Lobato (Galway WFC), Megan Mackey (Brighton & Hove Albion), Chloe Singleton (Galway WFC), Tiegan Ruddy (CCSU), Sinead Donavan (Galway WFC)
Forwards: Alannah McEvoy (Shelbourne), Carla McManus (Kilkenny United), Kelly Brady (World Class), Heather Payne (Bristol City), Niamh Reynolds (Reading) Michelle O'Driscoll (Daytona State University), Keelin McEntee (DLR Waves)
UEFA Women's Under-19 European Championship - Elite Round
03/04 - Hungary 0-4 Republic of Ireland
06/04 - Republic of Ireland v Serbia, Campo Municipal de A Lomb,. KO 13:00 (12:00 Irish time)
09/04 - Republic of Ireland v Spain, San Lázaro, Santiago de Compostela, KO 18:30 (17:30 Irish time)